Friday Cat-erpillar Blogging: Defensive Strikes

Caterpillars can be a bit “touchy”. Touching a caterpillar gently on its abdomen can elicit a “striking” behavior in which the caterpillar rapidly contorts its body and snaps at the point of contact with its mandibles. I once did a youth program that included both blowflies on sticks and caterpillars. The youth, paying more attention to their caterpillars than yours yours truly, found that touching the legs of the blowfly to the back of a caterpillar elicited a rapid strike response. The caterpillars respond just as well to a dead fly as a live one and will respond similarly to other types of contact.

The strike response is a defense against attack by insect predators and parasitoids. In nature, parasitoids are a major mortality factor for caterpillars. Deterring or even killing the parasitoid is an advantage to the caterpillar. The strike behavior is a reasonably good defense. Scientists who grow the parasitoid, Cotesia, in the laboratory have found that immobilizing the larva so it cannot strike will decrease mortality of the parasitoid adult and increase the rate of parasitism.

Tobacco Hornworm Caterpillar

There are a lot of questions concerning how a caterpillar directs its strike and the accuracy. Griethuijsen and colleagues have found that the accuracy depends on the location of the “attack”. Strikes directed toward a touch on the posterior abdomen were more accurate than strikes directed toward the anterior portion of the abdomen. The process that caterpillars use to direct their strike is a mystery, especially with regard to the receptors and signals that the caterpillar utilizes. Understanding the guidance system may have practical applications for robotics.

*Spatial accuracy of a rapid defense behavior in caterpillars. Linnea I. van Griethuijsen, Kelly M. Banks and Barry A. Trimmer. J Exp Biol 216, 379-387. February 1, 2013
doi: 10.1242/jeb.070896

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.

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2 Responses to Friday Cat-erpillar Blogging: Defensive Strikes

Sam says:

February 7, 2013 at 8:45 pm

It is very interesting to know that the caterpillars we received in my ENTM 105 class as part of our pet bug project do have a defense mechanism that they use quite often. Now that I know about this strike behavior I will be more aware of not touching my caterpillar and be more careful when transporting it to bigger living conditions when it runs out of its food supply.

meredith says:

February 11, 2013 at 6:31 pm

I found the ancedote about the children and their blowfiles and caterpillars especially interesting, in that the caterpillars responded exactly the same to both dead and living flies. The response mechanism, then, is a reaction to touch that might be threatening-not a concious response to a perceived and understood threat. Somehow, the nerves controlling the response are beyond the caterpillar’s controll, like the regulation of the human heartbeat.