The hairworms can be confused with the mermithid nematodes, which also parasitize insects. The latter have pointed ends to their tapered bodies. Locomotion consists of bending and writhing movements. Males can swim in a crude, undulatory manner. The eggs are deposited in the water in long, gelatinous strings, which swell and sometimes exceed the size of the female, containing several million eggs.
Adults die after mating and egg laying.
The eggs hatch in 15 to 80 days, depending upon temperature. The larva is unlike the adult, having a protrusible proboscis armed with spines. It has a very brief free-swimming existence as the larvae usually encyst on the surface of vegetation, etc., at or near the water's edge within 24 hours of hatching. The cysts remain viable for a month or more on moist vegetation adjacent to or in the water. Within the host, the larva digests and absorbs surrounding tissues as nourishment.