Arachnids and Horseshoe Crabs (Chelicerata) – LIFE IN THE LOWER SUSQUEHANNA RIVER WATERSHED

May 19, 2026May 25, 2026

The Stewards of Inland Shorebird Habitat

As they travel between coastal wintering ranges and breeding territories in Canada and Alaska, vast numbers of shorebirds pass through the lower Susquehanna region each spring and fall—though few stop here to rest, feed, and provide us with an opportunity to observe them. Prior to the construction of man-made dams and other alterations on our lotic (flowing) waterways including the river, shorebirds took advantage of lateral bars, stream deltas, and other alluvial deposits as places to loaf and re-energize. Before they were drained and filled, some of the valley’s wetlands probably included sparsely vegetated flats where shorebirds could drop in for a brief visit. Previous to their extirpation from our region, North American Beavers were the primary providers of quality habitat for shorebirds and other migrating waders on our lotic waters. Their widespread network of dams, pools, and marshes maximized floodplain function by keeping streams thoroughly connected to their wetlands, nurturing plant communities that not only provided food and shelter for the beavers and other wildlife, but provided superb buffering against erosion while protecting against sediment and nutrient imbalances in lower Susquehanna waterways.

Beaver Dam and Lodge — Beaver dams need not be large, particularly on low-gradient streams where a structure like this is sufficient to create a pool with depth adequate for building and maintaining a lodge and transporting leafy branches and other food items by water.

A beaver lodge assembled in a pool with less than three feet of water, deep enough to provide the family with a measure of protection against terrestrial predators.

Beaver Pool — Beaver pool ecosystems provide homes for hundreds of species of plants and animals, including migrating shorebirds and other waders.

Mud flats in the margins between emergent shrubs and herbaceous plant growth attract migrating shorebirds like this Solitary Sandpiper to the abundance of invertebrate life. Seasonal movements of migrating shorebirds regularly coincide with the reductions of water levels in beaver pools which typically occur between May and September each year.

During its southbound migration in September, a Least Sandpiper searches for arthropods and annelids as it visits a food-rich puddle along the periphery of a beaver pool.

A Pectoral Sandpiper feeds in shallow water near a stand of Common Cattails in a beaver pool.

During migration, rails including the Sora are attracted to dense emergent vegetation in beaver pools. Some will nest in these rodent-managed refugia.

Green Herons visit beaver pools during migration and, due to the reliability of the food supply, will often nest in their vicinity.

So how did this happen? How did the North American Beaver become a keystone species—an animal upon which the majority of other life forms within its ecosystem are so reliant? Well, it’s largely due to the fact that our beavers aren’t particularly fond of a constant stream of noise. More specifically, they don’t like the sound of running water in places where they intend to build and maintain a lodge. And so, as they begin to place sticks, mud, limbs, stones, and other materials within a noisy riffle on a stream, they create a dam, and behind it a pool—a pool that is particularly advantageous for protecting their home and providing a means of conveyance for their construction materials and food supplies.

Cascading Series of Beaver Pools — On a high-gradient segment of stream, beavers will create a cascading series of pools. Because water filters through a beaver dam instead of spilling over it, the work of these meticulous rodents soon silences the sounds of water changing altitude. No more sonorous riffle.

Beaver Dam — **Quiet please.** High seasonal stream flow and damage from storms may create areas where water begins to erode the structure of the dam. Where this condition persists, an adult beaver will soon mend the breach, just to quiet things down. Why would beavers demand such a hush upon their domain? Well, they have poor eyesight, but their hearing is excellent, and they rely upon it to detect danger.

The Louisiana Waterthrush (Parkesia motacilla), one of our earliest-arriving warblers, nests in forests along clear, high-gradient streams. In mid-April, we found this individual and three others squabbling over a breeding territory adjacent to the series of cascading beaver pools shown in the previous images.

Brook Trout and Blacknose Dace — Native denizens of coldwater streams, neither the Brook Trout nor the Eastern Blacknose Dace has any difficulty finding its way through the voids in beaver dams to ascend and descend the sequence of pools.

Beaver Dam and Pool on Low-gradient Stream — On a low-gradient segment of stream, a dam just over a foot in height may be sufficient to create a beaver pool of considerable size. Resembling the water-logged muskeg of the far north, well-established beaver pools form boggy habitats familiar to migrating shorebirds.

Water levels in the pools usually drop along with the stream’s base flow as soon as the effects of the spring thaw and rain showers subside. Feeding areas in shallow water and on muddy ground are often revealed just in time for northbound shorebirds and other waders to stop by in late April and May. These conditions often persist through the growing season and the fall migration of these birds which begins as early as late June and sometimes extends into October.

Tree Swallow at Natural Cavity — Where the pool inundates standing timber such as Red Maple and other species not used by beavers, the dead snags provide vital feeding areas for birds and other wildlife. Cavity nesters like this Tree Swallow seldom find suitable natural housing elsewhere.

Eastern Newts Among Alderfly Exuvia — The mosaic of marshlands and braided stream channels within the beaver pool complex supports an abundance of aquatic life including these breeding Eastern Newts, seen here surrounded by the exuvia left behind following a massive hatch of alderflies (Sialinae). Alderflies are a stream inhabitant during their larval stage and are indicator of clean water conditions.

**A modern-day example of the way fully functional stream floodplains used to look in the Lower Susquehanna River Watershed.** Though the pools may appear pond-like during the cooler and wetter months of the year, by summer the water levels behind the beaver dams recede as the base flow of the stream wanes. Now the true nature of the marsh, shallow pool, and braided stream complex is revealed. Unlike most man-made dams that set a fixed pool elevation regardless of flow by discharging water over the top of the structure or through a spillway or gate, beaver dams merely throttle the flow through their porous construction. Unless the beaver begins plugging small leaks as fast as the stream flow ebbs, the water level in the pools will drop. So they’re not left high and dry, lodges are located in the deepest pools, usually in close proximity to the dam and/or one of the stream courses. Though not inundated during the dry season, the soil in the pool complex is almost always damp and plants grow vigorously there, sequestering nutrients and retaining sediments in beneficial deposition patterns that actually inhibit erosion of the riparian landscape. These streams and floodplains retain their hyporheic zone and freely exchange water with the underlying water table and aquifer. It’s the ultimate floodplain management system, and the beavers don’t even know their doing all the work. (Google Maps base image)

Where another high-gradient segment of stream enters the main pool complex, beavers have created an additional series of cascading pools. The impoundments created by these dams help diffuse stormwater energy and process more nutrients and sediments within the floodplain’s wetland vegetation system. (Google Maps base image)

Sandhill Cranes in Beaver Pool — Beaver pools often refill as stream flows increase following autumn rains. The stockpiles of vegetative foods that grew within the beaver’s domain through the summer then become flooded and are a prime source of nutrition for not only the beavers, but waterfowl during both their autumn and spring migrations. Gleaning and probing Sandhill Cranes often find these habitats to their liking as well.

While North American Beavers have returned to the region, most live as “bank beavers”, residing in the river and larger creeks of the valley where they excavate shelters among the roots of Black Willows and other shoreline trees and shrubs. Floodplain encroachment, legacy sediment deposits, and just plain human intolerance have all conspired to prohibit North American Beavers from performing their magic on smaller local streams. For migrating shorebirds, this continued absence of beaver dam ecosystems has turned much of the lower Susquehanna valley into “flyover country”. Those travelers that do stop to rest and feed concentrate at the few favorable locations such as the lateral bars and the hydroelectric dam-created delta at the Conejohela Flats on the river in Lancaster County. But centralization has its drawbacks. Migrants spending time at concentration points may have a greater chance of contracting and spreading disease. Protracted heavy foraging can degrade these habitats. And over time, features such the lateral bars and delta deposits, including those on the Conejohela Flats, transition into other habitats—riparian forests. A more widespread selection of favorable stopover points for shorebirds, waders, waterfowl, and other migrants is certainly desirable.

IMITATION IS THE SINCEREST FORM OF FLATTERY

Until public sentiment sways in favor of the North American Beaver, wildlife managers are mimicking some of the attributes of their sound-inspired installations.

New Impoundment at Middle Creek Wildlife Management Area — Created by excavating a depression in heavy clay soils, this new impoundment at the Pennsylvania Game Commission’s Middle Creek Wildlife Management Area collects water directly from rainfall and from surface runoff. Its depth at no point is greater than about two or three feet. During the driest times of the year, this space will be a mudflat, and a haven for migrating shorebirds.

Shallow-water conservation impoundments designed, constructed, and managed for migratory waterfowl and waders including shorebirds are not what we typically refer to as ponds—though they are lentic (still) waters. Similar shallow freshwater impoundments at our National Wildlife Refuges are referred to as pools by the United States Fish and Wildlife Service, but smaller versions like this example at Middle Creek very closely resemble the prairie potholes created by glacial scour in the north-central United States and adjacent portions of Canada. Many populations of migratory birds are familiar with pothole ecosystems and, like the beaver pools and marshes, have relied upon them as waypoints along their journeys for centuries.

Pond and Lake Zonation — Impoundments most beneficial to migrating waterfowl and waders including shorebirds are shallow in depth. They lack the deeper waters of a pond or lake and thus have no limnetic (open water) or aphotic zones. Managed throughout as a littoral zone, impoundments grow plants in shallow water or on damp soil through the summer months to chew up nutrients accumulated in waste deposited by visiting birds. This vegetation is then flooded from late fall through early spring as forage habitat for migratory waterfowl. The timing of the fluctuations in water levels approximates those of the beaver pools and marshes on lotic (flowing) waters.

Impoundment Gate — A gate assembly is a water control structure installed to provide seasonal management of the water levels in a conservation impoundment. More than once, beavers have heard the sounds of tumbling waters inside these types of devices and tried to dam them up!

You’ve heard the line, “If you build it, they will come.” Well, it’s true. Here is a sample of the activity witnessed during the past two weeks at the new impoundment completed just several months ago at Middle Creek Wildlife Management Area along the tour route just beyond the “Stop 3” overlook.

The ubiquitous Snow Geese were among the first migratory occupants of the new impoundment. A few are currently lingering in the vicinity.

Ducks soon followed. These Blue-winged Teal were among the last to pass through earlier this month.

Wilson's Snipe — Wilson’s Snipe were among the first species of migratory shorebirds to visit the new impoundment at Middle Creek…

…as were Killdeer, a species which nests nearby.

Then, earlier this month, flocks of shorebirds including these Least Sandpipers were arriving to feed and rest.

Least Sandpiper and a Semipalmated Sandpiper — A Least Sandpiper (left) and a Semipalmated Sandpiper (right).

White-rumped, Least, and Solitary Sandpipers — Here’s a Solitary Sandpiper (right) feeding alongside a Least Sandpiper (center) and a White-rumped Sandpiper (left).

Least Sandpiper and a White-rumped Sandpiper — A Least Sandpiper (left) and a White-rumped Sandpiper (right).

Rare in our area during spring, the White-rumped Sandpiper (Calidris fuscicollis) flies north using the central flyway, then heads south along the Atlantic flyway in the fall, when it tends to be more regular here.

Rocking and teetering along as it looks for food, the Spotted Sandpiper may be one of the easiest of shorebirds to identify.

Chunky little Dunlin (Calidris alpina) with their conspicuously down-curved bills are another easy-to-identify species, particularly in the spring when their breeding (alternate) plumage includes a black belly.

Black-bellied Plovers acquire a handsome set of plumage in the spring as well.

The Semipalmated Plover doesn’t have nearly the flair for ornament its close relatives the Killdeer do; these little shorebirds wear only one ring around their neck instead of two. Think this plover is cute?,…

Speaking of legs, here’s one of dozens of Lesser Yellowlegs that visited the new impoundment during their recent northbound travels.

Though less numerous than the smaller Lesser Yellowlegs, a Greater Yellowlegs seldom goes unnoticed when dropping by the man-made pothole habitat.

Wilson's Phalarope — Everyone likes to see something unusual every now and then, and this impoundment delivers. Just yesterday, we photographed this migrating Wilson’s Phalarope (top center) among two Least Sandpipers (top left and right), a Lesser Yellowlegs (left and slightly forward of the phalarope), and a White-rumped Sandpiper (foreground).

Species of wildlife in addition to shorebirds and waterfowl have already found the new impoundment favorable…

Pairs of breeding Spot-winged Gliders (Pantala hymenaea), seen here in tandem while ovipositing, were swarming the impoundment after arriving earlier this week. These dragonflies are ofttimes unpredictable nomads and are similar in appearance to the usually more numerous Wandering Gliders. To recolonize seasonal portions of their range, both are famous for hitching a ride en masse on storm systems. They share the behavior of finding ephemeral and new bodies of water favorable for egg laying due to their low density of aquatic predators.

We watched this Snapping Turtle arrive to apparently find the newly created waters to its liking. Snapping Turtles are important consumers in a wetland ecosystem. Larger specimens may fill the role of an upper trophic level or apex predator, eliminating vulnerable mid-level consumers including other Snapping Turtles.

Because it bounces its tail up and down like a Spotted Sandpiper, you may at first glance mistake an American Pipit for a shorebird. Long known as the Water Pipit, these songbirds have been visiting the impoundment while migrating north and stopping to feed in nearby croplands.

Seen here with Least Sandpipers is a visiting Glossy Ibis.

Western Cattle Egrets visiting Middle Creek this spring have been frequenting the new impoundment.

Western Cattle Egret — With still little in the way of insects such as grasshoppers available in the surrounding landscape,…

…cattle egrets are looking to find prey like this Green Frog.

Managing saturation levels in shallow-water impoundments to resemble the seasonal variations in beaver pool and marsh systems can create lush growth and wildlife-rich environments. Take a look at some images from a project in a headwaters area of a tributary to Conewago Creek (west)…

Well-established Shallow-water Impoundment — By late July, southbound shorebirds were already using these mudflats to feed and rest. Other sections of the impoundment were dense with emergent and aquatic plants, the latter kept hydrated in deeper pools of the project by the inflow from several captured springs that supplement direct rainfall and sheet runoff to supply its water. During a seasonal drawdown, the exposure of the impoundment’s soils to direct sunlight can provide a measure of disinfection to reduce the chances of disease transmission among its populations of visiting birds and other animals.

Water Lily Growth — In the deeper pools of the impoundment, water lilies and other aquatic plants grow in lush mats to provide cover and feeding areas for resident populations of breeding reptiles and amphibians.

Immature Little Blue Heron — …and this immature Little Blue Heron, a wanderer typical of more southern latitudes.

While walking the road among tall grasses in the supporting landscape surrounding this impoundment, we were at first startled when these Sandhill Cranes strode by going the other direction. We quietly kept moving,…

Sandhill Cranes with Colt — The hatching of this colt is testimony to the vital role wetland ecosystems play in the lives of hundreds of species. Whether they be beaver pools and marshes on lotic waters or man-made shallow lentic waters, each of these habitats is filling a void that left floodplains and other critical lowland biomes faltering. While they can’t replace the full-function floodplain management provided by an active beaver colony, shallow-water impoundments can provide relief for habitat-starved populations of the animals and plants that rely upon them. A constellation of these projects on lands public or private across the lower Susquehanna watershed could help provide refuge for many of our flora and fauna with the most desperately fragmented of ranges.

So that you can relax while observing the comings and goings at a pair of the lower Susquehanna valley’s man-made impoundments, the Pennsylvania Game Commission has erected two viewing pavilions for public use on its lands…

The Haldeman Island observation pavilion is located on State Game Lands 290 just upstream from the Juniata River’s mouth on the Susquehanna at Clark’s Ferry in Dauphin County.

Haldeman Island Pavilion — It overlooks not only the island’s man-made shallow-water impoundments and neighboring grasslands, but the tower used in the 1970s to reintroduce Bald Eagles from Saskatchewan to the lower Susquehanna. Interpretive signs explain the conservation stories of habitats and the eagle reintroduction program.

Middle Creek W.M.A. Observation Pavilion — The observation pavilion at Middle Creek Wildlife Management Area is of similar construction to the one at Haldeman Island. It is accessed from the parking pull-off along the tour road at its intersection with Chapel Road, just before the right turn and incline that leads to the “Stop 3” grassland overlook.

It too includes numerous interpretive signs to help visitors understand impoundment management.

During the next two weeks, the exodus of migrating shorebirds now staged and feeding upon Atlantic Horseshoe Crab eggs on Delaware Bay will commence. During the evening of their departure from the bay, many of these birds cross portions of the Lower Susquehanna River Watershed, particularly east of the river. Stormy weather and other climatic conditions may force some of them to seek a place to put down temporarily, so keeping a close eye on the new pothole-like impoundment at Middle Creek may be a prudent move. After that, waders known as “post-breeding wanderers” can show up at any time. Then, beginning as early as late June, shorebirds begin moving south on a migration that can provide us with viewing opportunities into September and beyond. See you out there!

July 6, 2025

Sorry, But We Have No Steamed Crabs Today

Earlier today, we collected some mint leaves from the garden to make a batch of iced tea. Just prior to plunging them into boiling water, we noticed this Goldenrod Crab Spider (Misumena vatia) hiding in the foliage.

May 25, 2025June 27, 2025

Deer Tick or Dog Tick?

Deer Tick vs. Dog Tick — Several weeks back, we removed the tick on the left from the editor’s neck. Upon returning from an outing earlier today, he discovered the one on the right crawling up his sock. It’s almost like they’re out to get him, so after tossing the day’s apparel into the washer, it was time to hit the showers posthaste. Because where there’s one, there are more. And you absolutely never want to spend the night with a tick.

May 15, 2025May 15, 2025

Photo of the Day

White-tailed Deer Button Buck Hosting Engorged Ticks — When it comes to sitting down and watching an episode of Hollywood Squares or indulging in a game of Tic-Tac-Toe, those of us here at susquehannawildlife.net are quick to play right along. But when it comes to mixing it up with a Tick-Backed Doe or a Tick-Backed Buck like this one, you can count us out. Upon finding this button buck infested with engorged Deer Ticks and heading our way on a grassy trail, we decided to turn around and limit our walk to the gravel roadway where there was less of a chance of picking up any hitchhikers from the vegetation where this guy has been spending his time.

May 6, 2025May 6, 2025

Singing in the Rain

Neotropical birds are fairly well acquainted with repetitive periods of thundershowers. With that in mind, we decided not to waste this stormy Tuesday by remaining indoors.

Utility Right-of-way with Successional Habitat — We hiked this utility right-of-way to the north of a heavy thunderstorm and found plenty of activity in the shrubby successional habitat there.

Rain or shine, male Indigo Buntings were busy singing. All this exuberance is intended not only to establish and defend a nesting territory…

Prior to the implementation of the intensive manicuring practices we see currently applied to most utility right-of-ways, shrubby thickets filled miles of these linear corridors to create a webbed network of early successional growth throughout the lower Susquehanna valley. Loss of this specialized habitat has led to the almost total elimination of the formerly common Blue-winged Warbler as a breeding species here.

Another Neotropical species that nests in successional thickets is the Prairie Warbler (Setophaga discolor), seen here during one of this morning’s downpours.

The Hooded Warbler is fond of wooded thickets along the edge of forested land such as those in the Third/Stony Mountain utility right-of-way.

We hope you enjoyed our walk in the rain as much as we did. If you venture out on a similar excursion, please remember this. The majority of the wild animals around us have busy lives, particularly at this time of year. Most don’t take a day off just because it rains—that includes ticks.

Female Deer Tick — Be certain to check yourself for ticks, especially these very small Deer Ticks (Ixodes scapularis), also known as Black-legged Ticks. Deer Ticks are vigilantly looking for something to latch onto, even in the rain, and they can be vectors of Lyme disease. We found this adult female as a stowaway on the editor’s neck just before heading home from today’s stroll.

August 31, 2024August 31, 2024

A Prescribed Fire Site After the Burn

Back on March 24th, we took a detailed look at the process involved in administering prescribed fire as a tool for managing grassland and early successional habitat. Today we’re going turn back the hands of time to give you a glimpse of how the treated site fared during the five months since the controlled burn. Let’s go back to Middle Creek Wildlife Management Area for a photo tour to see how things have come along…

Prescribed Fire application in March — Pennsylvania Game Commission crews administering prescribed fire on a grassland demonstration site back on March 16.

Prescribed Fire Site in May — By late May, native herbaceous perennial wildflowers including Joe-pye Weed had re-greened the site. One of the goals of the burn was to kill fire-sensitive woody plants, thus preventing the process of succession from reforesting the site.

Yellow-breasted Chat in May — Because prescribed fire is administered in a mosaic pattern that permits some early successional growth to remain until the next burn, birds including this thicket-nesting Yellow-breasted Chat are able to take advantage of the mixed habitat during their breeding season in May and June.

Prescribed Fire Site in August — By August, the site is a haven for native plants and animals.

Native Warm-season Grasses and Wildlflowers in August — The burn has promoted the growth and late-summer bloom of fire-tolerant native wildflowers and warm-season grasses…

Indiangrass in Flower — …including Indiangrass,…

Thin-leaved Coneflower, a plant also known as Brown-eyed Susan. — …Thin-leaved Coneflower (Rudbeckia triloba), a plant also known as Brown-eyed Susan,…

…and Joe-pye Weed, a plant butterflies find irresistible.

Eastern Tiger Swallowtail collecting nectar from Joe-pye Weed.

Black-morph Eastern Tiger Swallowtail — A black-morph Eastern Tiger Swallowtail collecting nectar from Spotted Knapweed (Centaurea steobe micranthos), a non-native invasive plant found growing in an area of the burn site missed by this year’s fire. While many non-native plants are unable to survive the flames and heat produced by prescribed fire, it isn’t an absolute cure-all. It doesn’t eliminate all invasive plants, it just keeps them from dominating a landscape by out-competing native species. Left unmanaged, Spotted Knapweed is a tough perennial invasive that can easily become one the species able to overtake a vulnerable grassland. It can be a stubborn survivor of some prescribed burns. On the plus side, butterflies really like it.

By August, native grassland plants in the prescribed fire area were already providing an abundance of seeds for birds including this American Goldfinch.

For larger birds like turkeys and pheasants, an abundance of Carolina Grasshoppers are providing a protein-dense food source in managed grasslands.

And tiny flying insects, a nuisance to us as we take a stroll alongside the grasslands, are a meal taken on the wing by dragonflies including this Black Saddlebags.

Elsewhere around the refuge at Middle Creek, prescribed fire and other management techniques are providing high-quality grassland habitat for numerous species of nesting birds…

Bobolinks nested both in areas subjected to controlled burns…

Bobolink in Hay Field — …and in hay fields where mowing was delayed until the nesting season, including the fledging process, was completed earlier this month.

As advertised, Grasshopper Sparrows nested in these fields as well.

We hope you enjoyed this short photo tour of grassland management practices. Now, we’d like to leave you with one last set of pictures—a set you may find as interesting as we found them. Each is of a different Eastern Cottontail, a species we found to be particularly common on prescribed fire sites when we took these images in late May. The first two are of the individuals we happened to be able to photograph in areas subjected to fire two months earlier in March. The latter two are of cottontails we happened to photograph elsewhere on the refuge in areas not in proximity to ground treated with a prescribed burn or exposed to accidental fire in recent years.

Eastern Cottontail at a site subjected to prescribed fire earlier in the spring.

These first two rabbits are living the good life in a warm-season grass wonderland.

Eastern Cottontail with ticks. — Eastern Cottontail at a site not subjected to any recent fire activity.

Oh Deer! Oh Deer! These last two rabbits have no clock to track the time; they have only ticks. Better not go for a stroll with them Alice—that’s no wonderland! I know, I know, it’s time to go. See ya later.

May 28, 2024June 15, 2024

Pest Control at the Picnic

During one of the interludes between yesterday’s series of thunderstorms and rain showers, we had a chance to visit a wooded picnic spot to devour a little snack. Having packed lite fare, there wasn’t enough to share. Fortunately, pest control wasn’t a concern. It was handled for us…

This young American Toad (Anaxyrus americanus) patrolled the grounds of the grove gobbling up any creepy crawlies it happened to encounter.

Though spotted nearby, none of these traditional picnic crashers, possibly Big-headed Ants (Pheidole species), made it through the toad’s dragnet.

What had this Eastern Black Carpenter Ant (Camponotus pennsylvanicus) so frustrated during its attempt to spoil our affair?

Decaying Tree Stump — …so it’s back to gnawing on this rotting stump for you!

We spied this curious little Crab Spider (Tmarus species) searching the benches for tiny invertebrates.

Then, at the corner of the table, we found this Running Crab Spider (Philodromus species) clutching what appeared to be two ofttimes pesky, but harmless, flying insects called non-biting midges (Chironomidae).

After enjoying our little luncheon and watching all the sideshows, it was time to cautiously make our way home,…

January 22, 2024January 22, 2024

Birds Along the River’s Edge

Just as bare ground along a plowed road attracts birds in an otherwise snow-covered landscape, a receding river or large stream can provide the same benefit to hungry avians looking for food following a winter storm.

Here is a small sample of some of the species seen during a brief stop along the Susquehanna earlier this week.

Along vegetated edges of the Susquehanna and its tributaries, the Song Sparrow is ubiquitous in its search for small seeds and other foods. As the river recedes from the effects of this month’s rains, the shoreline is left bare of more recently deposited snow cover. Song Sparrows and other birds are attracted to streamside corridors of frost-free ground to find sufficient consumables for supplying enough energy to survive the long cold nights of winter.

Thousands of American Robins have been widespread throughout the lower Susquehanna valley during the past week. Due to the mild weather during this late fall and early winter, some may still be in the process of working their way south. Currently, many robins are concentrated along the river shoreline where receding water has exposed unfrozen soils to provide these birds with opportunities for finding earthworms (Lumbricidae) and other annelids.

This Golden-crowned Kinglet was observed searching the trees and shrubs along the Susquehanna shoreline for tiny insects and spiders. Temperatures above the bare ground along the receding river can be a few degrees higher than in surrounding snow-covered areas, thus improving the chances of finding active prey among the trunks and limbs of the riparian forest.

Not far from the kinglet, a Brown Creeper is seen searching the bark of a Silver Maple (Acer saccharinum) for wintering insects, as well as their eggs and larvae. Spiders in all their life stages are a favorite too.

American Pipits not only inhabit farm fields during the winter months, they are quite fond of bare ground along the Susquehanna. Seen quite easily along a strip of pebbly shoreline exposed by receding water, these birds will often escape notice when spending time on mid-river gravel and sand bars during periods of low flow.

An American Pipit on a bitterly cold afternoon along the Susquehanna.

July 24, 2023August 25, 2023

Shorebirds and More at Bombay Hook National Wildlife Refuge

Have you purchased your 2023-2024 Federal Duck Stamp? Nearly every penny of the 25 dollars you spend for a duck stamp goes toward habitat acquisition and improvements for waterfowl and the hundreds of other animal species that use wetlands for breeding, feeding, and as migration stopover points. Duck stamps aren’t just for hunters, purchasers get free admission to National Wildlife Refuges all over the United States. So do something good for conservation—stop by your local post office and get your Federal Duck Stamp.

2023-2024 Federal Duck Stamp. Your Federal Duck Stamp is your free pass to visit the nation's National Wildlife Refuges including Bombay Hook National Wildlife Refuge on Delaware Bay near Smyrna, Delaware. — Your Federal Duck Stamp is your admission ticket for entry into many of the country’s National Wildlife Refuges including Bombay Hook National Wildlife Refuge on Delaware Bay near Smyrna, Delaware.

Still not convinced that a Federal Duck Stamp is worth the money? Well then, follow along as we take a photo tour of Bombay Hook National Wildlife Refuge. Numbers of southbound shorebirds are on the rise in the refuge’s saltwater marshes and freshwater pools, so we timed a visit earlier this week to coincide with a late-morning high tide.

This pair of Northern Bobwhite, a species now extirpated from the Lower Susquehanna River Watershed and the rest of Pennsylvania, escorted us into the refuge. At Bombay Hook, they don’t waste your money mowing grass. Instead, a mosaic of warm-season grasses and early successional growth creates ideal habitat for Northern Bobwhite and other wildlife.

Shearness Pool at Bombay Hook N.W.R. — Twice each day, high tide inundates mudflats in the saltwater tidal marshes at Bombay Hook prompting shorebirds to move into the four man-made freshwater pools. Birds there can often be observed at close range. The auto tour route through the refuge primarily follows a path atop the dikes that create these freshwater pools. Morning light is best when viewing birds on the freshwater side of the road, late-afternoon light is best for observing birds on the tidal saltwater side.

A Great Blue Heron at high tide on the edge of a tidal creek that borders Bombay Hook’s tour route at Raymond Pool.

Semipalmated Sandpipers stream into Raymond Pool to escape the rising tide in the salt marsh.

Semipalmated Sandpipers and Short-billed Dowitcher — More Semipalmated Sandpipers and a single Short-billed Dowitcher (Limnodromus griseus) arrive at Raymond Pool.

Two more Short-billed Dowitchers on the way in.

Sandpipers, Avocets, Egrets, and Mallards — Recent rains have flooded some of the mudflats in Bombay Hook’s freshwater pools. During our visit, birds were often clustered in areas where bare ground was exposed or where water was shallow enough to feed. Here, Short-billed Dowitchers in the foreground wade in deeper water to probe the bottom while Semipalmated Sandpipers arrive to feed along the pool’s edge. Mallards, American Avocets, and egrets are gathered on the shore.

Semipalmated Sandpipers, Short-billed Dowitchers, and Forster's Terns — Hundreds of Semipalmated Sandpipers, several Short-billed Dowitchers, and some Forster’s Terns (Sterna forsteri) crowd onto a mud bar at Bear Swamp Pool.

Semipalmated Sandpipers, Forster's Terns, and a Short-billed Dowitcher — A zoomed-in view of the previous image showing a tightly packed crowd of Semipalmated Sandpipers, Forster’s Terns, and a Short-billed Dowitcher (upper left).

Short-billed Dowitchers, American Avocets, and a Snowy Egret in Raymond Pool. A single Stilt Sandpiper (Calidris himantopus) can been seen flying near the top of the flock of dowitchers just below the egret.

Stilt Sandpiper among Short-billed Dowitchers — Zoomed-in view of a Stilt Sandpiper (Calidris himantopus), the bird with white wing linings.

American Avocets probe the muddy bottom of Raymond Pool.

Dunlin and Short-billed Dowitchers — Among these Short-billed Dowitchers, the second bird from the bottom is a Dunlin. This sandpiper, still in breeding plumage, is a little bit early. Many migrating Dunlin linger at Bombay Hook into October and even November.

Marsh Wren singing — The chattering notes of the Marsh Wren’s (Cistothorus palustris) song can be heard along the tour road wherever it borders tidal waters.

Marsh Wren Nest — This dome-shaped Marsh Wren nest is supported by the stems of Saltwater Cordgrass (Sporobolus alterniflorus), a plant also known as Smooth Cordgrass. High tide licks at the roots of the cordgrass supporting the temporary domicile.

By far the most common dragonfly at Bombay Hook is the Seaside Dragonlet (Erythrodiplax berenice). It is our only dragonfly able to breed in saltwater. Seaside Dragonlets are in constant view along the impoundment dikes in the refuge.

Red-winged Blackbirds are still nesting at Bombay Hook, probably tending a second brood.

Mute Swans and Canada Geese — Non-native Mute Swans and resident-type Canada Geese in the rain-swollen Shearness Pool.

A pair of Trumpeter Swans (Cygnus buccinator) as seen from the observation tower at Shearness Pool. Unlike gregarious Tundra and Mute Swans, pairs of Trumpeter Swans prefer to nest alone, one pair to a pond, lake, or sluggish stretch of river. The range of these enormous birds was restricted to western North America and their numbers were believed to be as low as 70 birds during the early twentieth century. An isolated population consisting of several thousand birds was discovered in a remote area of Alaska during the 1930s allowing conservation practices to protect and restore their numbers. Trumpeter Swans are slowly repopulating scattered east coast locations following recent re-introduction into suitable habitats in the Great Lakes region.

A hen Wood Duck (second from right) escorts her young. — Wood Ducks in Bear Swamp Pool.

Black-necked Stilt and young. — A Bombay Hook N.W.R. specialty, a Black-necked Stilt and young at Bear Swamp Pool.

As the tide recedes, shorebirds leave the freshwater pools to begin feeding on the vast mudflats exposed within the saltwater marshes. Most birds are far from view, but that won’t stop a dedicated observer from finding other spectacular creatures on the bay side of the tour route road.

Tidal Marshes — Bombay Hook National Wildlife Refuge protects a vast parcel of tidal salt marsh and an extensive network of tidal creeks. These areas are not only essential wildlife habitat, but are critical components for maintaining water quality in Delaware Bay and the Atlantic.

The shells of expired Atlantic Horseshoe Crabs were formerly widespread and common among the naturally occurring flotsam along the high tide line on Delaware Bay. We found just this one during our visit to Bombay Hook. Man has certainly decimated populations of this ancient crustacean during recent decades.

Boardwalk Trail — As the tide goes out, it’s a good time for a quick walk into the salt marsh on the boardwalk trail opposite Raymond Pool.

Among the Saltmarsh Cordgrass along the trail and on the banks of the tidal creek there, a visitor will find thousands and thousands of Atlantic Marsh Fiddler Crabs (Minuca pugnax).

A male Atlantic Marsh Fiddler Crab peers from its den.

A juvenile Clapper Rail (Rallus crepitans crepitans) emerges from the cover of the cordgrass along a tidal creek to search for a meal.

Great Black-backed Gulls, Herring Gulls, and possibly other species feed on the mudflats exposed by low tide. — Great Black-backed Gulls, Herring Gulls, and possibly other species feed on the mudflats exposed by low tide in the marshes opposite Shearness Pool.

Ospey — An Osprey patrols the vast tidal areas opposite Shearness Pool.

No visit to Bombay Hook is complete without at least a quick loop through the upland habitats at the far end of the tour route.

Blue Grosbeaks (Passerina caerulea) are common nesting birds at Bombay Hook. This one was in shrubby growth along the dike at the north end of Shearness Pool.

Trumpet Creeper and Poison Ivy — These two native vines are widespread at Bombay Hook and are an excellent source of food for birds. The orange flowers of the Trumpet Vine are a hummingbird favorite and the Poison Ivy provides berries for numerous species of wintering birds.

Pileated Woodpecker in Sweet Gum — The Pileated Woodpecker is one of the numerous birds that supplements its diet with Poison Ivy berries. The tree this individual is visiting is an American Sweetgum (Liquidambar styraciflua), a species native to the Atlantic Coastal Plain in Delaware. The seed balls are a favorite winter food of goldfinches and siskins.

Red-bellied Slider and Painted Turtle — Finis Pool has no frontage on the tidal marsh but is still worth a visit. It lies along a spur road on the tour route and is located within a deciduous coastal plain forest. Check the waters there for basking turtles like this giant Northern Red-bellied Cooter (Pseudemys rubiventris) and much smaller Painted Turtle.

The White-tailed Deity is common along the road to Finis Pool.

Fowler's Toad — Fowler’s Toads (Anaxyrus fowleri) breed in the vernal ponds found in the vicinity of Finis Pool and elsewhere throughout the refuge.

Turk's Cap Lily — The National Wildlife Refuge System not only protects animal species, it sustains rare and unusual plants as well. This beauty is a Turk’s Cap Lily (Lilium superbum), a native wildflower of wet woods and swamps.

Just as quail led us into the refuge this morning, this Wild Turkey did us the courtesy of leading us to the way out in the afternoon.

We hope you’ve been convinced to visit Bombay Hook National Wildlife Refuge sometime soon. And we hope too that you’ll help fund additional conservation acquisitions and improvements by visiting your local post office and buying a Federal Duck Stamp.

March 26, 2023

Photo of the Day

A male Deer Tick — It’s so tiny, you can’t even feel it crawling on your skin. It’s the Deer Tick (Ixodes scapularis), also known as the Black-legged Tick, and it’s already looking for someone to latch on to. Don’t let it be you. After your foray outdoors, be certain to shower and conduct a full body search for these little hitchhikers. Then, remember to launder the clothing you were wearing. Deer Ticks in the Lower Susquehanna River Watershed frequently transmit Borrelia burgdorferi, the bacteria that causes Lyme disease, and can be vectors of other microbiological pathogens as well. The specimen in this photograph is an adult male. Adult females are similar, but the edge of the abdomen has a crescent-shaped reddish border. The nymphal stage tick, which is half the size of an adult, is even more likely to infect humans with the Lyme disease bacteria, so be extra vigilant.

April 17, 2022April 22, 2022

Photo of the Day

Spiders of the Lower Susquehanna River Watershed: "Tiger" Wolf Spider — A “Tiger” Wolf Spider (Tigrosa species) lurks beneath the doorstep at the susquehannawildlife.net headquarters. These arachnids reach only about one inch in length but appear startlingly larger due to their husky build. To feed, Wolf Spiders spin no web for snagging flying insects. Instead, they keep watch with their eight eyes, then ambush or chase down suitable prey. If handled roughly or pinched between an object such as a shoe and your skin, Wolf Spiders can inject a sore-producing venom. We like having them around our entranceway, just to keep a few eyes on things.

October 24, 2021November 4, 2021

A Visit to the Post Office, for Just One Stamp

It’s been more than a year and a half since Uncle Tyler Dyer has been on one of our outings. He’s been laying low, keeping to himself—to protect his health. So he was quite excited when we made our way to the Delaware coast to have a look at some marine and beach life at Cape Henlopen State Park.

Uncle Ty hadn’t visited the Atlantic shoreline here for almost two decades, and he was more than a bit startled at what he saw…

Cape Henlopen State Park has spectacular wild dunes and pine forests, but notice how clean the high-tide line is on the beach. This is not a good sign. During our walks, we found not one mollusk shell (clam, scallop, snail, etc.), skate egg case, whelk egg case, dead fish, or other sign of benthic life from the adjacent surf and sea.

We found the remains of Mole Crabs (Emerita talpoida), also known as sand fleas, a crustacean that burrows into the surf-washed sands of the beach, but there were no signs of life from deeper waters.

One of a dozen or so Lesser Black-backed Gulls (Larus fuscus) observed consuming Mole Crabs. There was little else for these birds to eat. Sanderlings (Calidris alba) and other shorebirds typically found foraging along the surf’s edge were totally absent.

Atlantic Ghost Crabs (Ocypode quadrata) live in the predominantly dry sands of the beach, above the high tide line. Missing were the remains of aquatic crabs, including Atlantic Horseshoe Crabs (Limulus polyphemus), and other invertebrates that are often found washing in with the tide.

If you want to see an Atlantic Horseshoe Crab, you may have no better option than to visit the aquariums at the state park’s nature center.

A nearly sterile beach might be delightful for barefoot sunbathers and the running of the dogs, but Uncle Ty isn’t the barefoot type. He likes his sandals and a slow peaceful stroll with plenty of flora and fauna to have a look at. We could tell he was getting bored. So we headed home.

Along the way, Uncle Ty asked to stop at the Post Office. He wanted to get a stamp. Thinking he was going to fire off a terse letter of protest to the powers that be about what he saw at the beach, we obliged.

Soon, Uncle Ty trotted down the steps of the Post Office with his stamp.

Uncle Tyler Dyer with his one stamp. The 2021-2022 Federal Duck Stamp is available at most local Post Offices. According to the United States Fish and Wildlife Service, ninety-eight percent of the $25 purchase price goes directly to acquiring and protecting wetland habitat.

Uncle Ty bought a duck stamp, so naturally we asked him when he decided to take up hunting. He explained, “Man, I gave that stuff up when I was thirteen. I’ve got the Thoreau/Walden mindset—hunting is something of an adolescent pursuit.”

It turns out Uncle Ty bought a duck stamp to support wetland acquisition and improvements, not only to benefit ducks and other wildlife living there, but to improve water quality. In Delaware, tidal estuary restoration work is underway at both the Prime Hook and Bombay Hook National Wildlife Refuges on Delaware Bay. These projects will certainly enhance the salt marsh’s filtration capabilities and just might improve the populations of benthic life in the bay and adjacent ocean at Cape Henlopen.

Uncle Ty tossed the stamp atop the dashboard and we were again on our way, but we weren’t going directly home. We made a stop along the way. A stop we’ll share with you next time.

May 21, 2021June 3, 2025

They’re Here

The Magi have arrived. Emanating from the shadows of a nearby forest, you may hear the endless drone of what sounds like an extraterrestrial craft. Then you get your first look at those beady red eyes set against a full suit of black armor—out of this world. The Magicicada are here at last.

This exuvia, the leftover from a cicada’s final molt, tells us they are here.

A Brood X Periodical Cicada soon after emergence and final molt.

Not to worry, cicadas are harmless and docile when handled. This is Magicicada septendecim, the largest and most common of our three species of Brood X seventeen-year cicadas. They are currently emerging along south-facing borders of forests and wooded parks and lawns.

Magicicada septendecim can be recognized by the orange on the thorax behind each eye and in front of the wing insertions. The smaller M. cassini and M. septendecula have no orange coloration between the eye and wing.

Magicicada septendecim (seen here) has broad orange stripes on the abdomen. M. cassini has an all black abdomen and M. septendecula, the rarest species, has narrow well-defined orange stripes.

If you go out and about to observe periodical cicadas, keep an eye open for these species too…

Spotted Lanternflies, one of our most dreaded invasive species, have hatched. These tiny nymphs about 5 millimetres in length were found feeding on a Virginia Creeper (Parthenocissus quinquefolia), a native vine in the grape family (Vitaceae).

Deer Ticks, also known as Black-legged Ticks, are hanging around on vegetation of all kinds looking to hitch a ride on a suitable host. Don’t let it be you. This adult female, less than 5 millimetres in length, was washed loose during an after-hike shower.

December 21, 2019October 4, 2023

Some Autumn Insects

With autumn coming to a close, let’s have a look at some of the fascinating insects (and a spider) that put on a show during some mild afternoons in the late months of 2019.

Bush Katydids (Scudderia species) are found in brushy habitats and along rural roadsides. Their green summer color fades to brown, maroon, and gold to match the autumn foliage where they hide. Bush katydids often remain active until a hard freeze finally does them in.

The Eastern Buck Moth (Hemileuca maia) is fuzzy, appearing to wear a warm coat for its autumn expeditions. Adults emerge in October and may fly as late as December. Females deposit their eggs on the twigs of Bear Oak (Quercus ilicifolia), Blackjack Oak (Q. marilandica), or Chestnut Oak (Q. montana), trees that, in our region, seem most favorable for the moth’s use when growing on burned barrens and mountain slopes. The spiny caterpillars are known to feed only on the foliage of these few trees. In the lower Susquehanna valley, the Eastern Buck Moth is rare because its specialized habitat is in short supply, and it’s all Smokey The Bear’s fault.

The Sachem (Atalopedes campestris) wanders north from the Atlantic Coastal Plain into the Susquehanna valley each summer. In some years they become the most numerous small orange butterfly of all, particularly around home gardens. The larvae will feed on Crabgrass (Digitaria species), but have not found success overwintering this far north. By November, adults begin to look pretty drab.

From 1978 through 1982, the Asian Multicolored Lady Beetle (Harmonia axyridis) was introduced into the eastern states by the United States Department of Agriculture. It has become a nuisance in many areas where it swarms, sometimes bites, and often overwinters in large smelly masses within homes and other warm buildings. As you may have guessed, it’s possibly displacing some of the less aggressive native lady beetle species.

On a chilly afternoon, a sun-warmed Bold Jumping Spider (Phidippus audax) pounced and dispatched this sluggish worker Honey Bee (Apis mellifera) that was trying to gather pollen from a late-season Purple Coneflower bloom. This spider is bold indeed.

Under bridges, inside bird nest boxes, and sometimes beneath porches, the female Pipe Organ Mud Dauber (Trypoxylon politum), a predatory wasp, builds these elaborate nests composed of long rows (pipes) of nursery cells. Into each cell one or more paralyzed spiders is deposited along with one of the female’s eggs. When hatched, each larva will feed upon the paralyzed spider(s) inside its cell, then pupate. The pupae overwinter, then emerge from their cells as adults during the following spring. In the autumn, males often stand guard at an entrance to the nest to prevent parasitic species, including some flies (look at the fifth pipe from the right), from laying eggs on the pupae. These wasps are not aggressive toward humans.

A Black-and-yellow Mud Dauber (Sceliphron caementarium) observes a neighboring nest of Common Paper Wasps (Polistes exclamans). The Common Paper Wasp, a species also known as the Guinea Paper Wasp, is a native of the southern United States. It is currently expanding its range into the lower Susquehanna valley from the Atlantic Coastal Plain. These two wasp species and the Pipe Organ Mud Dauber are known to regularly coexist. All three will take advantage of man-made structures for their nest sites. People using the picnic tables beneath this pavilion roof never noticed the hundreds of docile wasps above.

Those moody Eastern Yellowjackets (Vespula maculifrons) can get very temperamental during warm autumn days. These wasps may appear to have no enemies, but away from areas impacted by man’s everyday activities, they do. The Robber Fly (Promachus species) hunts like a flycatcher or other woodland bird, waiting on a perch along the forest’s edge for prey to pass by, then ambushing it, yellowjackets included.

The invasive Spotted Lanternfly, a native of eastern Asia, continues to spread destruction. It established itself throughout much of the east side of the lower Susquehanna River during the summer and fall of 2019. Their route of travel across the farmlands of the region intersects with plenty of vineyards to obliterate and few, if any, natural enemies. Expect them to begin colonizing the west shore en masse during 2020.

In 2020, plan to roll a few Spotted Lanternflies over, enjoy the view, and wait for the crimson tide to pass. With any luck, they’ll peak in a year or two.

SOURCES

Eaton, Eric R., and Kenn Kaufman. 2007. Kaufman Field Guide to Insects of North America. Houghton Mifflin Company. New York, NY.

July 15, 2019July 16, 2019

Friendly Neighborhood Spider, Man

Within the last few years, the early-summer emergence of vast waves of mayflies has caused great consternation among residents of riverside towns and motorists who cross the bridges over the lower Susquehanna. Fishermen and others who frequent the river are familiar with the phenomenon. Mayflies rise from their benthic environs where they live for a year or more as an aquatic larval stage (nymph) to take flight as a short-lived adult (imago), having just one night to complete the business of mating before perishing by the following afternoon.

In 2015, an emergence on a massive scale prompted the temporary closure of the mile-long Columbia-Wrightsville bridge while a blizzard-like flight of huge mayflies reduced visibility and caused road conditions to deteriorate to the point of causing accidents. The slimy smelly bodies of dead mayflies, probably millions of them, were removed like snow from the normally busy Lincoln Highway. Since then, to prevent attraction of the breeding insects, lights on the bridge have been shut down from about mid-June through mid-July to cover the ten to fourteen day peak of the flight period of Hexagenia bilineata, sometimes known as the Great Brown Drake, the species that swarms the bridge.

An adult (imago) male Great Brown Drake (Hexagenia bilineata) burrowing mayfly. Adult mayflies are also known as spinners.

A sub-adult (based on the translucence of the wings) female burrowing mayfly (Hexagenia species). The sub-adult (subimago or dun) stage lasts less than a day. Normally within 18 hours of leaving the water and beginning flight, it will molt into an adult, ready to breed during its final night of life.

After so many years, why did the swarms of these mayflies suddenly produce the enormous concentrations seen on this particular bridge across the lower Susquehanna? Let’s have a look.

Following the 2015 flight, conservation organizations were quick to point out that the enormous numbers of mayflies were a positive thing—an indicator that the waters of the river were getting cleaner. Generally, assessments of aquatic invertebrate populations are considered to be among the more reliable gauges of stream health. But some caution is in order in this case.

Prior to the occurrence of large flights several years ago, Hexagenia bilineata was not well known among the species in the mayfly communities of the lower Susquehanna and its tributaries. The native range of the species includes the southeastern United States and the Mississippi River watershed. Along segments of the Mississippi, swarms such as occurred at Columbia-Wrightsville in 2015 are an annual event, sometimes showing up on local weather radar images. These flights have been determined to be heaviest along sections of the river with muddy bottoms—the favored habitat of the burrowing Hexagenia bilineata nymph. This preferred substrate can be found widely in the Susquehanna due to siltation, particularly behind dams, and is the exclusive bottom habitat in Lake Clarke just downstream of the Columbia-Wrightsville bridge.

Native mayflies in the Susquehanna and its tributaries generally favor clean water in cobble-bottomed streams. Hexagenia bilineata, on the other hand, appears to have colonized the river (presumably by air) and has found a niche in segments with accumulated silt, the benthic habitats too impaired to support the native taxa formerly found there. Large flights of burrowing mayflies do indicate that the substrate didn’t become severely polluted or eutrophic during the preceding year. And big flights tell us that the Susquehanna ecosystem is, at least in areas with silt bottoms, favorable for colonization by the Great Brown Drake. But large flights of Hexagenia bilineata mayflies don’t necessarily give us an indication of how well the Susquehanna ecosystem is supporting indigenous mayflies and other species of native aquatic life. Only sustained recoveries by populations of the actual native species can tell us that. So, it’s probably prudent to hold off on the celebrations. We’re a long way from cleaning up this river.

In the absence of man-made lighting, male Great Brown Drakes congregate over waterways lit often by moonlight alone. The males hover in position within a swarm, often downwind of an object in the water. As females begin flight and pass through the swarm, they are pursued by the males in the vicinity. The male response is apparently sight motivated—anything moving through their field of view in a straight line will trigger a pursuit. That’s why they’re so pesky, landing on your face whenever you approach them. Mating takes place as males rendezvous with airborne females. The female then drops to the water surface to deposit eggs and later die—if not eaten by a fish first. Males return to the swarm and may mate again and again. They die by the following afternoon. After hatching, the larvae (nymphs) burrow in the silt where they’ll grow for the coming year. Feathery gills allow them to absorb oxygen from water passing through the U-shaped refuge they’ve excavated.

Several factors increase the likelihood of large swarms of Great Brown Drakes at bridges. Location is, of course, a primary factor. Bridges spanning suitable habitat will, as a minimum, experience incidental occurrences of the flying forms of the mayflies that live in the waters below. Any extraordinarily large emergence will certainly envelop the bridge in mayflies. Lights, both fixed and those on motor vehicles, enhance the appearance of movement on a bridge deck, thus attracting hovering swarms of male Hexagenia bilineata and other species from a greater distance, leading to larger concentrations. Concrete walls along the road atop the bridge lure the males to try to hover in a position of refuge behind them, despite the vehicles that disturb the still air each time they pass. The walls also function as the ultimate visual attraction as headlamp beams and shadows cast by moving vehicles are projected onto them over the length of the bridge. Vast numbers of dead, dying, and maimed mayflies tend to accumulate along these walls for this reason.

The absence of illumination from fixed lighting on the deck of the bridge reduces the density of Great Brown Drake swarms. Some communities take mayfly countermeasures one step further. Along the Mississippi, some bridges are fitted with lights on the underside of the deck to attract the mayflies to the area directly over the water, concentrating the breeding mayflies and fishermen alike. The illumination below the bridge is intended to draw mayflies away from light created by headlamps on motor vehicles passing by on the otherwise dark deck above. Lights beneath the bridge also help prevent large numbers of mayflies from being drawn away from the water toward lights around businesses and homes in neighborhoods along the shoreline—where they can become a nuisance.

Lights out on the Columbia-Wrightsville bridge. Dousing the lights to eliminate fixed illumination on bridges is an effective method of reducing the density of *Hexagenia bilineata* swarms.

With the bridge lights darkened, male Great Brown Drakes, their cellophane-like wings illuminated by headlamps to appear as white spots on the road, number in the hundreds instead of hundreds of thousands in swarms on the bridge near the east and west shorelines.

Swarms of Great Brown Drake mayflies are still present at the Columbia-Wrightsville bridge, they’re just not concentrated there in enormous numbers. Evidence includes their bodies found in cobwebs along the entire length of the span.

The aptly-named Bridge Orb Weaver (Larinioides sclopetarius) constructs webs along the entire length of the Columbia-Wrightsville bridge, and on many of the buildings at both ends. The abundance of victims tangled in silk must overwhelm their appetite, or maybe they actually consume only the smaller insects. They have their choice. Of the Bridge Orb Weaver, Uncle Ty Dyer says, “When you live along the river, it’s your friendly neighborhood spider, man.”

The native Eastern Dobsonfly (Corydalus cornutus) is among the reliable indicators of stream quality in the Susquehanna at the Columbia-Wrightsville bridge. Winged adults, which live for about a week, are clumsy fliers attracted to lights. The aquatic larvae are known as hellgrammites, which require clean flowing water over rocky or pebbly substrate to thrive. Two adults were found on the bridge last evening. It would be encouraging to find more. Maybe we’ll stop back to have another look when the lights are back on.

SOURCES

Edsall, Thomas A. 2001. “Burrowing Mayflies (Hexagenia) as Indicators of Ecosystem Health.” Aquatic Ecosystem Health and Management. 43:283-292.

Fremling, Calvin R. 1960. Biology of a Large Mayfly, Hexagenia bilineata (Say), of the Upper Mississippi River. Research Bulletin 482. Agricultural and Home Economics Experiment Station, Iowa State University. Ames, Iowa.

McCafferty, W. P. 1994. “Distributional and Classificatory Supplement to the Burrowing Mayflies (Ephemeroptera: Ephimeroidea) of the United States.” Entomological News. 105:1-13.

July 31, 2017November 29, 2019

Digging In

If you visit the shores of the Susquehanna River during the warmer months of the year, there’s a pretty good probability that you’ll be taking a visitor along home with you. Not to worry, it won’t raid the icebox or change the television channels when you leave the room to get a snack. It won’t put you in the doghouse with the landlord for having a forbidden pet. As a matter of fact, you may not even notice your new companion. Sure enough though, it’s there, crawling through the luxurious warm fabric of your clothing and seeking out a good place to dig in and chow down. O.K., so now you’re worried.

Ticks, particularly the American Dog Tick (Dermacentor variabilis), are widespread in the Lower Susquehanna River Watershed. Like spiders, they are arachnids. They have a four-stage life cycle (egg-larva-nymph-adult) which, in the case of D. variabilis, requires a minimum of two months to complete. Females lay up to 6,500 eggs on the ground. Then the fun begins as the larvae with any hope of survival must attach to a small mammal to feed. They can survive for almost a year before finding a host. After a successful hookup and subsequent blood feast of up to two weeks duration, the larva drops to the ground, molts into a nymph, and finds another small mammal, usually a bit bigger this time, to feed upon. A nymph can survive for up to six months before needing to feed. Finding the second host, the nymph feeds for 3 to 10 days, then drops to the ground to molt into an adult. Adult American Dog Ticks can endure up to two years without feeding on a host. The adults mate and feed on larger mammals such as deer and domestic animals including, of course, dogs. After a blood meal of five days to two weeks duration, the adult female tick drops to the ground to lay eggs and initiate a new generation.

The adult American Dog Tick attaches to a potential host by hanging from vegetation and grabbing the passing victim with its forward legs to hitch a ride. If undetected, a female will find a nice warm spot and “dig in” to begin feeding. This male is looking for love, and in all the wrong places.

The American Dog Tick is renowned as a carrier of the Rocky Mountain Spotted Fever bacteria (Rickettsia rickettsii). The bacteria is vectored by the ticks from rodents to dogs and humans. The adult tick must be attached to the victim for a minimum of six to eight hours to transmit the pathogen. A rash spreading from the wrists and the ankles to other portions of the body begins two to fourteen days after infection.

Tularemia, caused by the bacteria Francisella tularensis, can be passed by the American Dog Tick. Symptoms can appear in three to twenty-one days and include chills, fever, and inflammation of the lymph nodes.

American Dog Ticks which attach to dogs, particularly near the neck, and are left in place to feed and engorge themselves for longer than five days can cause Canine Tick Paralysis. Symptoms usually begin to subside only after a recovery period following removal of the arachnid.

The American Dog Tick is exposed to Borrelia burgdorferi, the bacteria responsible for Lyme Disease, however, transmittal of this pathogen is by the smaller Deer Tick (Ixodes scapularis), also known as the Black-legged Tick. The Deer Tick is not presently common at Conewago Falls. In the adjacent uplands, it is widespread and is carrying Lyme Disease where the White-tailed Deity (Odocoileus virginianus), the preferred host for the ticks, is found along with mice and other small rodents, the source of B. burgdorferi bacteria. The Deer Tick easily escapes notice and cases of Lyme Disease are frequent, so vigilance is necessary.

SOURCES

Chan, Wai-Han, and Kaufman, Phillip. 2008. American Dog Tick. University of Florida Featured Creatures website entnemdept.ufl.edu/creatures/urban/medical/american_dog_tick.htm as accessed July 30, 2017.