MANHATTAN, Kan. – When the shrill buzzing of annual cicadas heralds the Dog Days of summer, entomologist Bob Bauernfeind can seem as intent as an old-time telegrapher. Rather than listening for dots and dashes, however, he’s identifying cicada species by sound.
Male cicadas produce the sounds by vibrating a pair of drumlike membranes in their abdomen. Although their method is the same, each one produces the distinct call of its particular species.
“Typically, the differences aren’t too difficult to discern. Knowing something about each species’ habits helps, too,” said Bauernfeind, who’s on faculty with Kansas State University Research and Extension.
The central United States is home to 17 species of cicadas.
The Dog-Day species that appear ever year belong to the genus Tibicen (T.), he said. They range widely in size. But, most are a rather large insect with clear wings that are long and well-veined. They have big, widely spaced eyes and a stocky body that’s usually green and brown -- sometimes tinged with red.
Bauernfeind added that the five largest and loudest choral groups in Kansas also have preferred habitats:
1. Trees (more or less) —
* T. pruinosus - sounds somewhat like a repetitive “zow-wie, zow-wie, zow-wie” -- sometimes with interruptions. This calling typically picks up and intensifies toward sunset.
* T. delbatusi and T. walkeri – produce a rapid, repetitive and uninterrupted “zwick-zwick-zwick-zwick.” In fact, they sound so much alike that even experts prefer to inspect them to identify species. (T. delbatus has lots of white, powdery wax –– pruinosity –– on its abdomen). Both species begin calling in the morning and continue well into the evening.
2. Grassy and shrubby areas —
* T. dorsata – calls with a raspy, throaty rattle. The loudest and largest (2 inches long) of the group, this cicada also is “wild,” readily taking flight when humans approach.
* T. aurifera – produces a piercing and unwavering “zzzzzzz” that begins somewhat quietly, gradually builds and then fades. It actively calls throughout the heat of the day, but stops after sunset. In direct contrast to T. dorsata, this species is not only the smallest (at 1.25 inches long) but also the easiest to capture by hand. It’s typically greenish, but a few “red phase” individuals can also occur.
Photos of all five species are on the Web at http://www.entomology.ksu.edu/Doc.aspx?id=4703.
Although they’re sometimes called annual cicadas, the Dog-Day species evidently have developmental cycles that range from two to five years, Bauernfeind said. They’re able to give the impression of having a one-year cycle because they produce overlapping generations with some appearing every year.
“Calling them annual cicadas can be useful, though, because it helps people separate their species from the cicadas that only emerge every 17 years in Kansas,” he said. “Those rarely seen species – the periodical cicadas -- are in an entirely different category on sound. They’re unbelievably loud and hard to hear as individual callers because they tend to emerge together by the millions.”
Their first glimpse of periodical cicadas convinced the earliest American colonists that they were being visited by a plague of locusts – similar to accounts in the Old Testament of the Bible. That misnomer has stuck ever since, Bauernfeind said, and often carries over as a misidentification for Dog-Day cicadas, too.
True locusts are a species of short-horned grasshoppers that sometimes dramatically increase in numbers, forming dark clouds as they migrate long distances in hungry, destructive swarms. In contrast, Dog-Day and periodical cicadas don’t move very far from where they’re born. They don’t feed on garden or agricultural crops, and they’re harmless to humans.
“Cicadas are just noisy and make some distinctive sounds,” the entomologist said. “Oh … and they leave a dry shell behind -- which is why people in some areas of the country used to call them ‘dry flies.’”
-30-