What do red concrete bugs look like?

Clover mitesI have these, too. When I was a kid we used to call them "bloodsuckers," since when smooshed, they left what appeared to be a smear of human blood. From what I've read, they are actually clover mites, and are harmless to humans. They like the concrete because it's warm, and they seek out warm conditions, swarming all over in spring to early summer.

They are in my house too, they call them red spider mites. They like warm weather and don't bite people only plants.