Quite a large quantity of black, flea-like insects ranging in size from sand grain sized to the size of a small tick. They seem to congregate around the median of the leaf, and cluster on the undersides. There are far fewer of them on the tops of the leaves. Thanks in advance for the help :)
My poppy has an infestation!
Probably aphids (aka plant lice), especially as I can see a syrphid fly larva in the second image; ones like that prey on aphids.
They look like black flea beetles... my sunflowers have been invaded by them this year :/
Flea beetles would not sit still for photos like the ones taken by totipotetence; they would start jumping off as soon as the plant was disturbed.