Host insects include larvae of many moths, butterflies, beetles, and especially sawfly larvae. Adult flies are often seen in flowers feeding on the nectar. They also consume honeydew secreted by various other insects, and then often parasitize the insect that produced the honeydew. They dart quickly when disturbed. Most flower flies feed on aphids, grasping their prey and sucking out the body fluids.
Some flower flies are parasitic, laying eggs on the eggs of harmful insects.
Larvae of the flower fly are slug-like and are found in plant leaves, in soil and in water. Both larvae and adults have insatiable appetites for aphids. Adult flies are about 15 mm. in length. You may not think of wasps as being beneficial insects, especially if you have ever been stung by one. In fact wasps are predators on many insects and their young.