While investigating leaf rollers and leaf miners as a part of our ongoing nature studies, we came upon a video on YouTube that perplexed me. Ten years ago (eeek, has it really been that long?) I had the remarkable opportunity to take part in an Earthwatch expedition to Ecuador, Rainforest Caterpillars. The focus of our assignment was on parasitism in caterpillars and while I am by no means an expert, I consider myself an insect enthusiast and can identify which insect order most specimens belong.
[ Edited :: This video has since been removed and I have been unable to find it – or a substitute.]
This video intrigued me because one of the things we did while in the field was ‘torment’ the caterpillars we found. Essentially, we would do this by gently petting them with a small paint brush and pinching them carefully with a pair of tweezers (enough to get a reaction but not to harm). We would then record their behavior or reaction to the stimuli. We did this to get a general idea of how the different species would defend themselves and observed a wide variety of behaviors including thrashing about, rearing up and attempting to bite the attacker (that would be us), as well as and most amusing,kicking frass at us.
The premise, as you’ll see when you watch the video, is that the caterpillars behave this way because they have been parasitized by a wasp and their behavior is not altered or controlled by the wasp. I didn’t think this was exactly the case. I thereby contacted the lead scientist with whom I worked and inquired about the validity of the video. His response confirmed my suspicion:
“This braconid genus, Glyptapanteles, is one that we rear a lot in Ecuador from geometrids. The video that you saw, and the paper in PLOS one about this is not necessarily that common. More generally, parasites do change the behavior of their hosts to the benefit of the parasites, but thrashing is still a very effective defense for most caterpillars against a broad array of predators and parasitoids.” ~ Lee Dyer
For your educational entertainment, I include this video showing a Tobacco Hornworm, Manduca sexta, caterpillar infested with parasitoids. The Braconid wasp, Cotesia congregate, lays its eggs in the body of the caterpillar, also depositing a virus which is thought to prolong the larval stages and prevent molting to the pupal stage. When the wasp larvae are mature, they burrow out through the caterpillar’s skin and make white silken cocoons on the surface. In this video, two newly emerged wasp larvae are spinning their cocoons.