Speaking of wasps, I just received this photo from Nan at Shady Grove Farm in Kentucky. The white things you see attached to a tomato hornworm are the pupae of a braconid wasp.
Using her ovipositor, the female braconid lays her eggs inside the body of the caterpillar. Once the eggs hatch, the larvae eat the insides of their host which, as you might imagine, is not good for the caterpillar. After the larvae mature, they eat through the skin of the caterpillar, attach themselves to the outside, and spin a cocoon. Eventually, the wasps mature and emerge as adults.
The Braconidae family is huge, containing perhaps 1700 species in North America. They are all parasitic on other insects or insect eggs. The adult wasps are small, usually less than a half-inch long.