Cowpea Aphid
Aphis craccivora
Observed at Eldoret Kenya. January 2014. The colony is on flower buds of cowpea (Kundee).
Because aphids can reproduce without mating, and bear live young that are already pregnant with the next generation, their populations can explode to immense size in a very short time. In the image at left notice that one aphid at top center appears darker and very swollen. This bug has likely been parasitized by an aphid wasp - soon an adult wasp barely 2 mm long will emerge from the aphid cadaver and begin parasitizing more aphids. It is when this and other natural enemies of aphids are disrupted that the aphids become serious pests of crops.