Probably fungus gnats. Hang a yellow fly strip, it will collect the adults. Go get some Gnatrol, that will get the larvae.

http://www.doityourself.com/stry/fungusgnats

If its not them, then I don't know.
Perp Reviewed by Perp on . little black nats underneath canopy little black nats how do i kill them/ what r they/?///////? Rating: 5