Caterpillars have it rough. For every butterfly that you see, countless more will have perished as either caterpillars or pupae at the hands of parasitic wasps. These wasps land on innocent caterpillars as they are contentedly munching away on leaves, inject their eggs into them and then fly away; the eggs hatch within the caterpillar and the wasp grubs voraciously eat their host from the inside out – whilst it is still alive.
But for some caterpillars, the misery doesn’t even end there. Enter Glyptapanteles, a wasp that deliberately leaves its caterpillar host alive after feasting on its innards, just to prolong its suffering. After the wasp larvae emerge from the caterpillar, they still need to metamorphose into adults and this leaves them vulnerable to ant attacks and even other types of parasitic wasps. To have a greater chance of surviving their pupal stage, therefore, the Glyptapanteles larvae make a zombie bodyguard out of the poor, half-eaten, barely-alive caterpillar.
The caterpillar spends the next few weeks curled up around the wasp cocoons. If another insect gets too close, the caterpillar flails around wildly in an attempt to repel the intruder. It may even spin protective silk over the wasp pupae, as seen in the picture above. The last of the caterpillar’s already drained energy goes into this task. When at last the wasps emerge as adults, the desiccated caterpillar finally dies. But why on earth does the caterpillar go to such great lengths to act as the babysitter for the same wasps that previously burrowed through its flesh?
It is, of course, being controlled by the wasp larvae. It is now nothing more than a mindless puppet, a true zombie. For years, though, scientists were puzzled as to how the larvae managed this mind-control when they were no longer inside the caterpillar’s body, but the latest studies indicate that at least a couple of larvae do stay behind inside their host to continue controlling its behaviour. Yet this is a suicide mission; the Glyptapanteles larvae still within the caterpillar’s body are doomed to die alongside their host, foregoing their own chance at pupating in order to protect the rest of their brood.