The beetles and flies are competing for the same resource. They both want to lay their eggs on the carcass so that their respective larva will have a ready source of food. In this competition, the beetles have a tiny, but powerful ally. Every beetle has a population of mites on its body. And as the beetle flies from carcass to carcass, the mites go along for the ride. And in return for the free air fare, the mites eat fly eggs from the carcass leaving it for the young beetles. The mites and the beetles enjoy a symbiotic relationship.