Tuesday, December 10, 2013

Grand Western Cicada

On this “True Bug Tuesday,” with Christmas carols seemingly always within earshot, I harken back to summer and the melodic sounds of cicadas. Ok, maybe “blaring noise” is a truer description of those members of the genus Tibicen that were omnipresent during our visits to Ohio, Iowa, and Kansas this year. One of the more impressive species we saw was the “Grand Western Cicada,” Tibicen dorsatus.

T. dorsatus is also known as the “Bush Cicada” and “Splendid Prairie Cicada.” Indeed, it is most abundant in remnants of tallgrass and shortgrass prairie, and savannah-like habitats in the Great Plains states east of the Rocky Mountains and west of the Mississippi River. Scattered records are also known as far east as Indiana. Few populations exist north of Wyoming and southern South Dakota.

This species is one of the so-called “annual” cicadas. That term translates to at least some individuals of a given species emerging as adults every year, even though the life cycle still takes about five years or more to complete. So, emergences are staggered, not synchronized as is the case with the periodical cicadas of the genus Magicicada. Annual cicadas also emerge later in the season than their synchronous relatives. Look for T. dorsatus in July, August, and September (as early as June in some southern latitudes).

The fact that annual cicadas are frequently heard during the hottest part of the summer and fall has lent them additional labels of “dog day cicadas” and “harvestflies.” They also present themselves during the hottest times of the day, depending on the species, adding a literal, audible sizzle to the infernal temperature.

Only male cicadas produce sound, and they do so internally. Most of the abdomen of a male cicada is occupied by two large cavities, each opening on the underside but covered by a lid-like “operculum.” Inside, a large muscle in each chamber can be vibrated at high speed, producing a sound that is amplified and projected outward as the insect contorts its body. The Little Drummer Boy has nothing on these guys.

Most of a cicada’s life is spent underground, of course, living as a hunchbacked nymph sucking plant sap from roots of trees and shrubs and other plants. That diet doesn’t foster rapid growth, and it therefore takes the insect a long period of time to mature. Eventually it does so, though, and claws its way to the soil surface, usually under cover of darkness, to complete its metamorphosis.

As soon as the nymph extracts itself from the ground, it seeks in earnest the nearest vertical object. Climbing to an adequate height (perhaps an individual decision rather than a hard-wired instinctive one) it digs in and splits its exoskeleton down the middle of its back. A soft, pale insect with stubby wings pulls itself out with great effort.

Many cicadas must perish in the act of this final molt, becoming tangled in their own “skin,” or simply not having enough energy to complete the ordeal. Others come out imperfect, unable to fly or with malformed legs. Those that do manage to struggle out of their old selves then hang quietly while the wings inflate and pigments begin to manifest themselves in the otherwise ghostly creature.

Once hardened, cicadas are durable insects. I once saw a Blue Jay catch a cicada in Cincinnati, Ohio, try to hammer it to death on a utility wire, only to have the insect slip out of its beak and fly away.

The Grand Western Cicada is one of our larger species, measuring around 57 millimeters (2.5 inches) from “nose” to the tips of its folded wings. The decorative white markings are actually waxy, and can rub off. The waxy substance also covers the belly of the insect, and cicadas often orient themselves belly-up to the sun so as to prevent becoming overheated.

While many cicada species also call from the canopy of trees, where they are shaded, the Grand Western Cicada often perches low on vegetation where it tends to be more exposed. Despite its contrasting coloration, it is surprisingly cryptic.

Another, very similar species, Tibicen tremulus, has recently been described. Its range overlaps with that of T. dorsatus, and the only way to easily segregate the two in the field is by differences in their songs.

This last summer was apparently a good year if you like cicadas. They were very abundant in the Midwest U.S. If you missed their diversity and concerts, keep an ear cocked for them next year.

Sources: Bartlett, Troy, et al. 2013. “Species Tibicen dorsatus - Bush Cicada,” Bugguide.net.
Cranshaw, Whitney, and Boris Kondratieff. 1995. Bagging Big Bugs: How to Identify, Collect and Display the Largest and Most Colorful Insects of the Rocky Mountain Region. Golden, CO: Fulcrum Publishing. 324 pp.
Hill, Kathy, and David C. Marshall. 2013. Insect Singers.
Salsbury, Glenn A. and Stephan C. White. 2000. Insects in Kansas (3rd Edition). Topeka, KS: Kansas Department of Agriculture. 523 pp.

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