This photo shows adult male (M) and female (F) Heligmosomoides. The name of this genus comes from the coiling of the body. These nematodes attach to the intestinal wall of their host by coiling around pieces of it, much like a boa constrictor. When live, these worms are red in color from the host blood that they have been feeding on. A typical female, at about 10-15 mm stretched, is about twice as long as a male. The posterior end of the female, at the lower left, is pointed. The male possesses a large copulatory bursa supported by muscular rays which help the male grip the female during mating.