Enters the Pawpaw Sphinx, Dolba hyloeus . Pretty cool caterpillar, dressed in brilliant green with diagonal white racing stripes down its side. It was happily munching away on a Pawpaw leaf, Asimina triloba. The one above is a healthy caterpillar. It will turn into a pretty pepper-colored moth.
A few leaves over was this poor guy. What are all those little tic-tac-like objects, you may ask? They are cocoons. Unfortunately for this caterpillar, a braconid wasp of the species Cotesia congregata discovered it. It oviposited, or laid its eggs, inside the caterpillar by inserting its ovipositor or "stinger" into the caterpillar's flesh. You can view this happening to another species of caterpillar here. Sounds pretty bad? Oh, it gets even better...
When the wasp injects the eggs, it also injects polydnavirus particles. These keep the caterpillar's immune system from destroying the eggs and also affects the behavior and the development of the caterpillar. And what do you think happens when those little larval braconid wasps hatch? Oh, yes, they eat the caterpillar's innards while it is still alive. Munch, munch, munch,...urp. Live food for the baby wasps; curtains for the caterpillar. This is worse than any horror movie I can think of...
Next the larvae emerge and make silken cocoons on the back of the zombified caterpillar. They ride around on the caterpillar that, in turn, keeps them safe. The polydnavirus sometimes affects the behavior of the caterpillar, so it will thrash around if any predator comes near the developing cocoons.
Adult braconid wasp, Cotesia congregata.
Photo by Ted Kropiewnicki.
Note the size is only about 3 mm.
And here is a photo that I found on BugGuide, showing the wasps emerging from the cocoons. The top of the silken cocoon pops open and out comes an adult braconid wasp. What really goes on in the insect world is much crazier than any far-fetched science fiction movie. Truly amazing!