Roundworms: Adenophorea

Physical characteristics: Mermis nigrescens worms are free living as adults. As larvae they are parasites that infect the body cavity of grasshoppers. These worms are thin and 2 to 8 inches (5 to 20 centimeters) long. Females are longer than males. Adult females are reddish brown at the front.

Geographic range: Mermis nigrescens (abbreviated as M. nigrescens) worms live in the British Isles, Europe, and North America. Specific distribution map not available.

Habitat: While they are larvae, M. nigrescens worms live mainly in grasshoppers and locusts but may also infect other insects. Once they burrow out of a host, the larvae dig into the soil, where they transform into adults.

Diet: M. nigrescens larvae feed on nutrients in their host. The free-living adults do not eat, so the worms must gain all of their nutrients while in the insect host.

Behavior and reproduction: Adult M. nigrescens worms easily climb plants, especially during rainy seasons. Females may stay in the soil for several years before coming out to lay eggs on grass and plants, which are then eaten by grasshoppers. Even though they sometimes move toward light, the worms die if they receive continued exposure to direct sunlight.

After the eggs hatch, M. nigrescens larvae bore through the host insect's intestinal wall into its body cavity and feed on the host's nutrients. Many worms can infect the same grasshopper. By late summer, the grasshopper is packed with the parasites and dies. The larvae leave the dead insect's body, and the worms spend the rest of their lives in the soil transforming into adults and growing to reproductive age.

Mermis nigrescens and people: Because the larvae kill their hosts, it may be possible to use M. nigrescens worms to control grasshoppers, which harm crops.

Conservation status: M. nigrescens worms are not considered threatened or endangered. ∎

While they are larvae, Mermis nigrescens worms live mainly in grasshoppers and locusts but may also infect other insects. Once they burrow out of a host, the larvae dig into the soil, where they transform into adults. (Illustration by Bruce Worden. Reproduced by permission.)