What would you feed a baby bat that you found?

I'm in that same position... I found a baby bat on the side of the road, and he wasn't flying.... so I brought him home & called the RSPCA. They said if he doesn't fly tonight then they'd come and get him tomorrow; but i feel bad for not feeding him. I gave him some water, but they apparently eat moths and little insects like that. The question is, how do i catch them for the baby?