Gordionus chinensis

Hairworms are known for their ability to make their host go for an impromptu (and terminal) swim in a stream or a pond, but by doing that they are not just sending ripples through the water, but also into the surrounding ecosystem. The paper we are looking at today features a species of hairworm from Japan call Gordionus chinensis - this parasite infects three different species of forest-dwelling camel crickets from the genus Diestrammena.

Photo by Danue Sachiko from here

The scientists who conducted the study that this paper is based on wanted to find out what happens to the the cricket population and their hairworm parasites after their home forest has been cut down. They conducted an observational field study at an experimental forest in the upper parts of the Totsu River at Nara Prefecture, Japan. The forest was originally clear-cut in 1912 and 1916 and since then, parts of it have been replanted and cut down at different point in time over the last century. Each study site corresponds with a different replanted forests of Japanese cypress ranging from 3 to 48 years old.

These scientists found that the camel crickets began returning a few years after a forest has been replanted, their abundance steadily increasing and eventually reaching a peak after the forest has been standing for at least 30 years. But their hairworm parasites did not return with similar gusto. In fact, they estimated that only second-growth forests that are more than 50 years old have hairworm populations that are as abundance as those found at undisturbed sites.

One possible reason for the hairworms' slow recovery is their complex life cycle which requires infection of more than one host. The replanted forest might be lacking some of the other host G. chinensis needs to complete its life cycle. Because parasites has such a negative public image, a forest which is free of parasites (or at least a specific parasite) might sound good to most people. But these hairworms actually play a very vital role in the ecosystem.

By causing their cricket host to jump into a stream, they actually serve as a kind of fast food delivery service for the fish living in those streams. A cricket infected with a hair worm is 20 times more likely to stumble into a stream and become fish food than an uninfected cricket - so fish which would not usually get to feed on such large land-loving insects on a regular basis can now do so thanks to the hairworm, and it has calculated that this straight-to-your-stream food delivery service accounts for 60% of the trout population's energy intake in some watersheds.

For hairworms, new forests just do not have the same creature comforts of old forests. And if you are a keen angler or simply appreciate a fish-rich stream - you have a parasite to thank for all the fishes.

Reference:
Sato, T., Watanabe, K., Fukushima, K., & Tokuchi, N. (2014). Parasites and forest chronosequence: Long-term recovery of nematomorph parasites after clear-cut logging. Forest Ecology and Management, 314: 166-171.