Praying mantises, like many insects, can harbor large internal parasites often mistaken for common worms. The sight of a long, thin organism emerging from a mantis demonstrates a complex parasitic relationship found in nature. This phenomenon illustrates how some parasites manipulate their hosts to complete their life cycle.
Identifying the Parasite
The organism observed exiting a mantis is not a true worm but a member of the phylum Nematomorpha, commonly known as a horsehair or Gordian worm. These parasites specialize in infecting arthropods, including crickets, beetles, and mantises. Their adult form is exceptionally long and thin, resembling a strand of horsehair, and they often coil into a knot-like mass.
Horsehair worms frequently reach lengths of four inches or more, with some species extending up to a foot. Their diameter remains extremely narrow, often measuring only about one-eightieth to one-tenth of an inch. Unlike true nematodes, adult horsehair worms lack a functional digestive system, absorbing nutrients directly through their cuticle while inside the host.
How the Mantis Becomes Infected
The horsehair worm life cycle begins when adults mate and lay eggs in water, such as streams or ponds. The eggs hatch into microscopic larvae that are capable of encysting if they are not immediately ingested by a suitable host. These larvae must then be consumed by an intermediate host, typically an aquatic insect larva like a mayfly or a chironomid.
The parasite remains dormant inside the intermediate host as it matures into a terrestrial adult insect. The praying mantis, a terrestrial predator, becomes the definitive host when it consumes this infected insect, such as a cricket or beetle. Once inside the mantis, the protective cyst dissolves, and the larval horsehair worm bores through the gut wall into the host’s body cavity.
Inside the mantis’s hemocoel, the larva develops into a mature worm, absorbing nutrients from the host’s tissues and growing significantly in size. This growth process can take weeks or months, during which the mantis may show no outward signs of infection. The mantis facilitates the parasite’s development until it reaches its final, reproductive stage.
Behavioral Changes and Host Outcome
Once the horsehair worm matures, it must return to water to reproduce and complete its life cycle. To achieve this, the parasite chemically influences the mantis to seek out and enter a body of water, a behavior known as hydrophilia. This behavior is unnatural for the typically terrestrial insect.
Research suggests the parasite achieves this by secreting proteins that mimic those used in the mantis’s nervous system, effectively hijacking its behavior. The worm may also alter the mantis’s perception of light, attracting it to the polarized light reflecting off the water surface. This induced march toward water ensures the parasite’s survival, as it needs an aquatic environment for reproduction.
When the mantis enters the water, the mature horsehair worm emerges from the host’s body, often through the posterior end. The emergence of the large worm, which can be several times the length of the mantis, typically results in the death of the host. The adult worm is now free to mate and start the cycle anew in its aquatic environment.
Are These Parasites Dangerous to Humans
Horsehair worms are highly host-specific, successfully parasitizing only arthropods. They pose no threat to humans, pets, or livestock. The parasitic stage of their life cycle depends entirely on the internal biology and environment of an insect host.
These organisms cannot survive or reproduce inside a mammalian host. While there have been rare instances of horsehair worms being accidentally ingested, they are considered pseudoparasites in vertebrates. If accidentally swallowed, the worms may cause only mild, temporary discomfort in the intestinal tract before being passed.