[barquar]

Originally Posted by harasseddad

Too late I fear. In a lovely bit of evolution, when the flies (which share the same genes as they came from the same parents) are ready to emerge, one of the larvae sacrifices itself and instead of emerging it moves into the brain of the caterpiller host. Once there it controls the caterpiller directly, making it move around to defend the fly cacoons against any enemies. The caterpiller is effectively dead, its body riddled with holes where the flies emerged and with a larvae in its brain - but it won't stop moving until the flies hatch - it's effectively a zombie.

Thanks for the info on the parasites Harassdad.
barquar