In considering microsize prey, one should see the issue from the perspective of their main predator, which is birds taking larvae to feed their chicks. Birds take a stupendous number of insect larvae to feed their chicks. One kind of defence is to eat food which is distasteful to birds. Many grubs put away ("sequester") poisonous compounds from the plants they eat. That makes them unpalatable to birds and their chicks. Another kind of defence is to be "not worth chasing", when the energy expended by the bird is not worth the energy gained by eating the prey. Micromoths and their microgrubs are not worth chasing for many birds. Thus they gain in having less rigorous predation from their main enemy. Much the same is true of microflies, which are also common. A similar argument explains that bats may go for larger, plumper flying adults where the energy gained is large compared to the energy spent catching them.