Just a guess but, If they jump they could be springtails. They usually live in the top inch or so of soil. Usually organic. Check and see when you water, if they leap around the surface. Springtails are somewhat of a debate. They eat decaying organic matter and some say they don't really effect grows (maybe even beneficial), but if there's a large enough infestation they may eat root (which of course means you have a root prob anyway). I had them in one grow and personally, they didn't really effect anything. How are the plants? What's your soil? Any pics?
