Suicidal Crickets

SQ FALL INSIDER 2020

written by JENNY NAMKOONG

illustrated by SVETLANA MCELWAIN

The night falls and crickets slowly emerge on the outskirts of a lake. They feed on other insects containing parasites that eventually grow to be cricket manipulators. Clouding the crickets’ rationality and inducing them to plunge into water, the parasites behave like mysterious lab inventions from sci-fi movies. Even with technological advancements every day, the thought of a living creature’s actions being controlled seems bizarre. Nonetheless, within our vicinity, these parasites commonly invade terrestrial arthropods like crickets and cause them to “blindly” scurry to water, dive, and meet death’s gate without hesitation.

Nematomorpha, more commonly known as Gordian or horsehair worms, are deadly parasites. Ranging from white, tan, brown to black colors, the peculiar creatures are found in both saltwater (Nectonematida) and freshwater (Gordiida). It is fascinating to see these long, thin, worm-like creatures squirm around their hosts’ body cavity until they are fully grown. Starting as small, white larvae, they can grow up to one meter in length by relying heavily on hosts for nutrients.

Nematomorpha initially enter aquatic insects like mayflies who serve as temporary hosts. Here, the parasites patiently wait for their temporary hosts to be consumed by their main hosts: terrestrial arthropods. There are diverse terrestrial arthropod species, but Nematomorpha most frequently enter crickets, grasshoppers, beetles and other common insects. As temporary hosts bridge Nematomorpha with main hosts, the parasites work their way up the food chain from aquatic insects to terrestrial arthropods. Finally, Nematomorpha burrow out the arthropods, wriggle into water, and fulfill their ultimate goal of reproduction. Nematomorpha must induce crickets to jump into water so their life cycle may be satisfied in an aquatic setting. While there are rare cases where these terrestrial arthropods survive, most main hosts drown in water and face death.

Nematomorpha begin and conclude their life cycle in aquatic environments. When a female Nematomorpha parasite produces strings of eggs, the eggs soon hatch into larvae and enter temporary hosts. As mentioned before, the temporary hosts are consumed by terrestrial arthropods, which then automatically also transition Nematomorpha to terrestrial arthropods, their key sites of growth. Nematomorpha develop into long, adult worms until they fill every square centimeter of their host’s body cavity. Of course, this is only possible because the parasites are flexible and able to bend or curve whenever necessary to fit in the hosts’ compact interior space. At their fully grown state, the parasites have an evolutionary drive to return to water, their only feasible site of reproduction. Controlled by Nematomorpha, crickets leap into water, drown, and remain helpless as these parasites pierce through the crickets’ exoskeleton. Once returned to their aquatic habitat, Nematomorpha mate and lay strings of eggs for the cycle to repeat.

There is no definite explanation regarding how the parasites alter crickets’ cognitive processes. Nonetheless, lab studies suggest that parasitic infections are related to changes in protein quantities. One such study compares protein and histology alterations that occur within crickets’ brains after Nematomorpha invasions. They discovered minimal protein alterations, and the study suggests these small differences occurred purely from the infection process, not Nematomorpha manipulation. However, the parasites also caused vast alterations in the crickets’ neuron productions, and the study suggests these changes in turn impacted the formation of cricket brain cell networks. The parasites likely hindered normal central nervous system activity of crickets and caused unsettling, abnormal brain functions for them to dive into water (Thomas et al., 2003). Overall, the lab reveals cricket behavior is altered by both the parasitic infection process and neural changes caused by Nematomorpha manipulation.

Despite the frightening effects Nematomorpha have on terrestrial arthropods, they have beneficial effects on the energy flows of ecosystems. According to a study from Japan, trout populations increased most rapidly during seasons when Nematomorpha brought arthropods to the aquatic environment. These arthropods became a major food source for the fish, thus boosting the trout populations (Sato et al., 2011). As a result, while Nematomorpha climb up the food chain for host invasions, Nematomorpha themselves also serve as an integral food source in the larger ecological food chain.

Although people may misjudge Nematomorpha as negligible worms due to their hair-like appearance, they carry the most threatening authority over crickets. They twist and turn to fill the hosts’ entire body and pierce through their exoskeleton after drowning them in water. Surprisingly, they are not sci-fi lab inventions but instead living organisms with an evolutionary drive to complete their life cycle. Their hazardous invasions and manipulations fortunately only impact invertebrates—so relax and rest assured!

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