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Cicadas and Their Killers

Jul 13, 2010

The middle of July through August is the time that we should be hearing annual, or dog-day, cicadas whining in the treetops around sunset. Sometimes they are referred to as locusts, but that name properly applies to another insect that is similar to a grasshopper. Annual cicadas should not be confused with the periodical cicadas, which are smaller and emerge on longer cycles (13 or 17 years).

Besides the noise, cicadas make their presence known by leaving their shed exoskeletons, or shells, on posts, tree trunks and other vegetation near where the bugs emerge from the soil. The shells are of brownish, translucent chitin and have a slit on the back where the molting adult insect slipped from its old skin. Having spent from two to five years underground in the dark soil sucking on roots for plant juices, I guess it’s understandable that they make a clamor when they finally see the light of day. The raspy singing of the males is part of their above-ground mission--to mate and lay the eggs for future generations of noise-makers. With only a few weeks to live as adults, any shy, quiet cicadas have no future in the gene pool. Mated female cicadas will lay their eggs in slits ripped into tree or shrub twigs, often weakening the young twigs and making them susceptible to breaking.

Meanwhile a giant wasp, the female cicada killer, patrols the air and paralyzes cicadas with her sting. She places her quarry in a ground nest as food for her developing larvae. The female wasps can be intimidating by their size, up to 2 inches long. They seldom will sting humans, however, unless handled roughly or stepped on. The smaller, male wasps act aggressively as they compete for the females, but males cannot sting. The female wasp often strikes flying cicadas, and I’ve seen the two insects fall from the sky to the ground in a fatal embrace (fatal at least for the cicada). Usually the cicada killer will win the fight and fly off with the cicada or drag it to her nearby nest. This aerial dogfight can go unnoticed to persons not aware of this predator/prey relationship. The cicada killers serve a useful purpose by helping to keep cicada populations in check. Cicadas help to aerate the soil and serve as food for birds as well as other predators. Their interaction with each other is one of many natural relationships that form a complex ecosystem.

Cicada killer photo by: Nancy Hinkle, University of Georgia, Bugwood.org

Comments

I just ran into this interesting blog after I republished a blog on identifying cicada songs on the Springfield Plateau Chapter Master Naturalists blog. There are additional cicada sound and video links at http://springfieldmn.blogspot.com/2010/07/dog-day-cicada.html

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