Wednesday, August 1, 2012

Cicada Killers, Human Friends

Wasps: one of the most feared groups of insects. They're also one of the most hated, namely because of the propensity of some species to sting. If you've found yourself at the business end of a wasp, you probably weren't too happy. If I had to venture a guess, I would say that this is how many people view wasps:

But perhaps wasps don't deserve such a bad reputation. Many species of wasps play important roles in the ecosystem, including parasitism of caterpillars and pollination of flowers. Some aren't aggressive towards humans, for example the Eastern Cicada Killer, Sphecius speciosus.

Intimidating at first, sure. But not a threat!

This wasp isn't interested in ruining our day. The male might be interested in us at first, but that's because he's curious: he patrols his territory looking for females. If something new moves in, he has to check it out to see if it's a female he can mate with. You know, kind of like a teenager. The males can't even sting, though they can jab you with a sharp spine. The females, however, are able to sting. But you'll have to punch it in the face while holding it to get it to sting you. No, these wasps are interested in game closer to their size...

Now we're talking!

If you haven't already figured it out by now, the Eastern Cicada Killer kills cicadas. Aptly named, no? The whole story is more intricate, however. First, the wasp needs to catch the cicada. She will fly around, searching for her prey, and then snatch it out of the air. Out comes her stinger, and boom: the cicada is paralyzed. Not killed, mind you--that would be too easy. She drags the cicada back to her sandy nest and deposits it in an earthen chamber, along with an egg. After that, she seals up the chamber and flies off to catch more cicadas. The female may have many egg chambers in her nest, all sealed and containing a cicada or two. 

Don't forget that throughout this process, the cicada is still alive, sealed in its tomb. What comes next? Death by grub. After the baby wasp hatches, it devours the warm, nutritious cicada and pupates. Overwintering comes next, and after it warms back up during the summer, the adult wasp emerges and continues the cycle anew. 

By killing cicadas, these wasps act as an ecological equalizer for trees. They remove cicadas from the environment, giving the trees a break from being nibbled on by the musical Hemipterans. On a related note, wouldn't it be fascinating to measure the population of the cicada killers after a periodical cicada emergence? Perhaps the influx of so many cicadas allows their own populations to explode, resulting in a whole bunch of cicada killers (and scared humans) the next summer. Of course, that's only if the cicada emergence coincides with when the cicada killers are active. 2016 is the next year for Brood V in Ohio, so keep your eyes open.

On a final note, in case you're wondering what the species name speciosus means, it's derived from the Latin for "showy" or "beautiful." Another apt description for this wasp.

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