The Hairworm Life Cycle
Hairworms are parasites of crickets and other arthropods that reside on all continents except Antarctica. There are two classes within the Phylum Nematomorpha that include the freshwater gordiids and the marine group known as the nectonematids. To date, over 350 species of freshwater hairworms and 5 marine species have been described.
Hairworms spend a portion of their life as a parasitic juvenile in an insect host. When they reach maturity, they demonstrate a fascinating behavior in which they manipulate their host to find water. At this time, their insect host, such as a cricket, begins wandering aimlessly in search of water. When the cricket encounters water such as a stream or pond, the cricket will jump in and the worm will expel itself from the cricket. On occasion, infected crickets may find themselves inside our homes and utilize pet water bowls for their hairworm's exit.
Eggs are laid in the water by female hairworms after mating. One species, Paragordius obamai, contains all females and was the first parthenogenic hairworm found in recent years (Hanelt, 2012). Life cycles vary slightly between species. For Paragordius varius, my study organism, the life cycle occurs faster than most others we know. For P. varius, eggs are laid in strings freely in the water. Eggs will hatch within two weeks and a small hairworm larvae (30 microns) will fall to the bottom of the water. Here they are ingested by invertebrates that feed on the bottom of the water column. Inside the invertebrate, the hairworm larvae forms a cyst, creating a protective shell or layer around itself. This larvae will only make it to adulthood if it can be carried to a terrestrial system. This is often accomplished by being ingested by small larval invertebrates who will leave the water to a terrestrial system and be consumed by a cricket host. Once inside the cricket, it excysts, removing itself from the protective layer, and begins to feed on the fat body organ of the cricket. Paragordius varius will reach adulthood inside the cricket within approximately 27-30 days (Hanelt, et al., 2005).
Credit: Ben Hanelt and Nematomorpha.net
Hanelt B, Bolek MG, Schmidt-Rhaesa A (2012) Going Solo: Discovery of the First Parthenogenetic Gordiid (Nematomorpha: Gordiida). PLoS ONE 7(4): e34472. doi:10.1371/journal.pone.0034472
Hanelt, B., F Thomas, A Schmidt-Rhaesa. 2005. Biology of the phylum Nematomorpha. Advances in Parasitology. 59: 243-305