There are parasitoid wasps that lay eggs inside other species of insect and have a symbiotic relationship with polydnaviruses that suppress the host's immune system so it doesn't attack the wasp eggs.
Basically, if you're an unlucky caterpillar, ant, or whatever, a wasp may come along, penetrate you with its girldick (ovipositor), and give you insect AIDS so that its young can hatch inside you and eat your still living flesh...