They are deadly enemies of small caterpillars, aphids, and other soft-bodied insects. The lowly ground beetle, so common under logs and debris, is another friend of man. Both larvae and adults are predaceous and feed on a wide variety of insects. Less common, but still important, robber flies are deadly enemies of grasshoppers, wasps, and other flies which they capture on the wing. Some of their prey are as large or larger than they are.
Tachinid flies are parasites of other insects.
This fly has laid its small white eggs just above the legs of the caterpillar in front of it. Upon hatching, the fly maggots will burrow through their hosts skin and feed on its internal organs. The caterpillar will die just as the larvae emerge and complete their development. In addition to these flies, many small wasps are important parasites of other insects. It is very difficult to measure how important these insects are, but there is no doubt that they are extremely valuable allies to us.