Aphids in the greenhouse

Aphids are a common problem, so it was just a matter of time before some wondered onto my greens.  At least that's what I'm telling myself now that I've found some lots.  Aphids are in the Homoptera order of the insect family.  Their distinguishing characteristic are two exhaust pipes, called cornicles, on their butts that secrete a warning scent when they are being attacked.  My camera is not powerful enough to take a picture of the cornicles, but you can see them here.