Filarial worms are nematodes that typically inhabit the body cavities and subcutaneous spaces of vertebrates. Most are viviparous (live-bearing) and their larvae, called microfilariae are found in the blood stream or subcutaneous space, where they are drawn up by biting insects when they feed. When the insects feed on a second host, the microfilariae are transferred and the life cycle starts again. Pelecitus fulicaeatrae is found in the leg joints of waster birds (coots and grebes) and its intermediate host is a louse, one more case of a parasite being the intermediate host of another parasite.
Contributed by Mike Kinsella and photo by Julia Diaz.