|Photo by Danue Sachiko from here|
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.
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.