Here is a case of one larva species preying on another. The little guys rearing up are rose sawfly larve which hatched from their egg cases in a rose bush yesterday. They are tiny! About a couple of mm. The other larva, perhaps that of a green lacewing, is preying on them. It had already consumed one of these guys, and now has another in its grip. The rose sawfly on the left of it, was repeatedly hitting it with its behind! Many sawfly larvae will form this S-shape when threatened.

These are on a rambling rose in my garden. I had them there last year so watched for them again this year. They are never abundant and they provide a lot of entertainment, so I just leave them alone. By the way, sawflies are not flies, but are in the wasp family.