Freeloader Fly (Milichiidae)

Probably one of the oddest insects I've ever photographed. They are known as kleptoparasites of predatory invertebrates. Another name for them is Jackal Fly. I found these on the kill of Black and Yellow Garden Spider (Argiope aurantia), a very large one I might add. The spider didn't seem to be bothered by their presence, or it may have just known it was useless to protest.