Identification of the Three Species of Brood X Periodical Cicadas

The emergence of Brood X Periodical Cicadas is now in full swing.  If you visit a forested area, you may hear the distant drone of very large concentrations of one or more of the three species that make up the Brood X event.   The increasing volume of a chorus tends to attract exponentially greater numbers of male cicadas from within an expanding radius, causing a swarm to grow larger and louder—attracting more and more females to the breeding site.

Holes in the ground where emerging Brood X Periodical Cicadas have come to the surface.
The exuvia of Periodical Cicadas that, following emergence from the soil, have ascended the trunk of an Eastern White Pine.  The exuvia is the exoskeletal remains of the cicada’s final molt from a nymph into a flying adult.

Each Periodical Cicada species has a distinctive song.  This song concentrates males of the same species at breeding sites—then draws in an abundance of females of the same species to complete the mating process.  Large gatherings of Periodical Cicadas can include all three species, but a close look at swarms on State Game Lands 145 in Lebanon County and State Game Lands 46 (Middle Creek Wildlife Management Area) in Lancaster County during recent days found marked separation by two of the three.  Most swarms were dominated by Magicicada septendecim, the largest, most widespread, and most common species.  However, nearly mono-specific swarms of M. cassinii, the second most numerous species, were found as well.  An exceptionally large one was northwest of the village of Colebrook on State Game Lands 145.  It was isolated by a tenth of a mile or more from numerous large gatherings of M. septendecim cicadas in the vicinity.  These M. cassinii cicadas, with a chorus so loud that it outdistanced the songs made by the nearby swarms of M. septendecim, seized the opportunity to separate both audibly and physically from the more dominant species, thus providing better likelihood of maximizing their breeding success.

Some of the tens of thousands of M. cassinii Periodical Cicadas in a concentration on State Game Lands 145 northwest of Colebrook in Lebanon County, Pennsylvania.  This swarm occupied deciduous and evergreen trees on several acres of a south-facing hillside.  To provide protection from predators and assure the chance of finding a mate “in the crowd”, lesser numbers of this and the rarer species, Magicicada septendecula, would need to merge into the swarms of the abundant M. septendecim Periodical Cicadas to breed.

The process of identifying Periodical Cicadas is best begun by listening to their choruses, songs, and calls.  After all, the sounds of cicadas will lead one to the locations where they are most abundant.  The two most common species, M. septendecim and M. cassinii, produce a buzzy chorus that, when comprised of hundreds or thousands of cicadas “singing” in unison, creates, when heard from a distance, a droning wail that can carry for a quarter of a mile or more.  It’s a surreal humming sound that may remind one of a space ship from a science fiction film.

Listen to the songs of individual cicadas at close range and you’ll hear a difference between the widespread M. septendecim “Pharaoh Periodical Cicada” and the other two species.  M. septendecim‘s song is often characterized as a drawn out version of the word “Pharaoh”, hence the species’ unofficial common name.  As part of their courtship ritual, “Pharaoh Periodical Cicadas” sometimes make a purring or cooing sound, which is often extended to sound like kee-ow, then sometimes revved up further to pha-raohM. cassinii, often known as “Cassin’s Periodical Cicada”, and the least common species, M. septendecula, often make scratchy clicking or rattling calls as a lead-in to their song.  Most observers will find little difficulty locating the widespread M. septendecim “Pharaoh Periodical Cicada” by sound, so listening for something different—the clicking call—is an easy way to zero in on the two less common species.

To penetrate the droning choruses of large numbers of “Pharaoh” and/or “Cassin’s Periodical Cicadas”, sparingly distributed M. septendecula cicadas have a noise-penetrating song consisting of a series of quick raspy notes with a staccato rhythm reminiscent of a pulsating lawn sprinkler.   It can often be differentiated by a listener even in the presence of a roaring chorus of one or both of the commoner species.  However, a word of caution is due.  To call in others of their kind, “Cassin’s Periodical Cicadas” can produce a courtship song similar to that of M. septendecula so that they too can penetrate the choruses of the enormous numbers of “Pharaoh Periodical Cicadas” that concentrate in many areas.  To play it safe, it’s best to have a good look at the cicadas you’re trying to identify.

M. cassinii Periodical Cicadas “singing” from a treetop at Colebrook, Lebanon County, Pennsylvania.  Clicking phrases are sure sign of the presence of this species and/or M. septendecula, the least likely of the three species to be encountered.  When in close proximity to a swarm, a listener will often notice the rising and falling volume of a chorus in a cycle that repeats every few seconds, an effect caused by cicadas attempting to synchronize their songs in a harmony with others in the group.  When courtship and mating is complete, female Periodical Cicadas will begin laying eggs in slits made in fresh new growth at the ends of branches on deciduous trees like the one seen here.

Visually identifying Brood X Periodical Cicadas to the species level is best done by looking for two key field marks—first, the presence or absence of orange between the eye and the root of the wings, and second, the presence or absence of orange bands on the underside of the abdomen.  Seeing these field marks clearly requires in-hand examination of the cicada in question.

Observing a perched Brood X Periodical Cicada can sometimes provide a view of the key field marks needed for identification of the species.  On the M. septendecim “Pharaoh Periodical Cicada” seen here, the orange patch between the eye and wing root and the orange bands on the underside of the abdomen are visible.
The abdomen of this perched M. cassinii “Cassin’s Periodical Cicada” appears, when viewed through the wings, to have orange bands.  But, examination in hand would show an all-black abdomen with glossy surfaces shining in the sunlight.  For accuracy, the up-close-and-personal look is necessary.
In the hand, cicadas can be better studied for key field marks.  M. septendecim (top) is larger than M. cassini (bottom) and M. septendecula, but the difference is not always apparent, particularly when a direct comparison cannot be made.

To reliably separate Brood X Periodical Cicadas by species, it is necessary to get a closeup view of the section of the thorax between the eye and the root (insertion) of the wings, plus a look at the underside of the abdomen.  Here’s what you’ll see…

Magicicada septendecim—“Pharaoh Periodical Cicada”

M. septendecim has an orange patch between the eye and the root of the wings.
The underside of M. septendecim’s abdomen has orange bands or stripes along the trailing edge of each segment. The width of the bands can vary, but is typically wider on males (left) than on females (right).

Magicicada cassinii—“Cassin’s Periodical Cicada”

The thorax of M. cassinii is black between the eye and the wing insertion.
The underside of M. cassinii’s abdomen is all black without orange bands or stripes in both the male (left) and female (right).

Magicicada septendecula

M. septendecula’s thorax is black between the eye and root of the wings.
The underside of M. septendecula’s abdomen has narrow orange bands or stripes along the trailing edge of each segment.  The width of the bands can differ.  Those of this male (left) are minimal and the bands on this female (right) are near the maximum for the species.

There you have it.  Get out and take a closer look at the Brood X Periodical Cicadas near you.

The abundant and widespread “Pharaoh Periodical Cicada” (M. septendecim).
It’ll all be over before long.  Accumulating remains of M. cassinii “Cassin’s Periodical Cicadas” beneath an Eastern White Pine at the site of the Colebrook State Game Lands swarm.

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