What looks like an aphid that’s ready to explode is actually what’s left over after being parasitized by a Braconid wasp (family Braconidae, subfamily Aphidiinae). Braconid wasps are tiny, only about 1/8 of an inch. Female wasps will attack aphids by injecting an egg inside a living aphid. When the egg hatches, the aphid serves as a living food source for the growing wasp larvae — slowly consuming the insides and eventually killing the aphid (called an endoparasite — consuming its prey from the inside). The wasp will pupate inside the “aphid mummy,” giving the deceased aphid a bloated body that is tan or golden in color. When the wasp pupates, it will chew a hole in the mummy’s abdomen and emerge.
Photo by Glenn Marangelo on 6/11/20 in Missoula, MT.