Attack of the Zombie Caterpillars!

My house is surrounded by zombies. No this isn’t some film script I’m working on, nor is it a video game I’m getting a little too into playing a la Tim Bisley, this is real life. However these are not the human flesh-eating zombie hordes of George A. Romero’s world, these are of a distinctly smaller and less terrifying nature, this is the insect world and this is the curse of the zombie caterpillar.

This year my front garden has been playing host to a whole lot of caterpillars. I even caught one for a few hours inside an empty ice cream tub in order to let my toddler take a good look (he was put back into some bushes when I realised my toddler’s greatest interest in the natural world was poking it). So when I noticed several of the yellow and black creepy crawlies hanging around my front door I wasn’t that surprised. What I did find rather odd was when I discovered about half a dozen of them had climbed up my door and proceeded to lay clutches of yellow eggs on it.

Let’s get one thing straight, a biologist I am not. Despite a childhood desire to be a forensic pathologist (thank you very much Agent Scully), I tend to find things of a biological nature a little, well, icky and have since happily retreated into the decidedly less gooey world of theoretical physics. However one thing I do recall quite clearly from my school days is the life cycle of moths and butterflies, and more precisely, the fact that caterpillars do not lay eggs. These egg laying caterpillars therefore had me intrigued and so I began a little research late one night to discover what exactly was going on, and what I discovered was far more fascinating than your common garden insect.

Ten minutes with my good friend Google provided me with the incredibly helpful website “Wild About Britain” and a quick search through their forums had me reading through a post from a member with the exact same situation as me, just two years previously. In hindsight, I rather wish I had not chosen to read this just before bed, and I suggest you bookmark the next bit for later reading if you plan to eat in the next hour. The replies to this post outlined the theory that this caterpillar was in fact the host to a clutch of eggs laid by a parasitic wasp, in fact a sort of mobile nursery. The wasp lays its eggs inside the caterpillar and when the larva hatch they eat the caterpillar from the inside out, avoiding the parts that keep it alive and functioning in a zombie form (well I did warn you about reading this close to mealtimes). The bright colours of the caterpillar ward off predators and help protect the larvae which are eventually laid outside the body -- the little piles of yellow blobs on my door. The forum also pointed to this fascinating article from New Scientist magazine which delves a little deeper into the biology behind this phenomenon, and also this rather amazing video that shows some rather violent and unexpected behaviour from the brainwashed caterpillars.

[youtube]http://www.youtube.com/watch?v=7UkDMrG6tog[/youtube]

I personally haven't witnessed any of this aggressive behavior from the caterpillars around my door, however that may be because I never witnessed them under threat. What I did get to see was a fascinating insight into a rather dark and macabre side of insect life, just thanks to taking a little time to look up what was happening quite literally on my doorstep. Sometimes you don’t need to go very far to discover something truly amazing.

First photograph provided thanks toJames Rose on Flickr.