The horsehair worm is a parasite that lives in water, and its larvae infect insects. Every year or two, a panicky client finds one of these in a toilet bowl, water dish, or a bit of pet vomit. They do not infest the pets, but the crickets or beetles may be eaten by a pet, and the worm puked up. If the insect enters the water, the mature parasite will exit to begin its life cycle anew.
There is really no harm in them (unless you’re the unlucky insect). I’ve kept this specimen in a test tube for years . If you stretched it out, it would be eight inches long.
This fall, we have been plagued by an unusually large influx of crickets as the weather cooled off. They apparently come inside to get warm. There have always been a few in the fall, but
hardly enough to notice. This year they have really been annoying. One of the elementary schools called in an exterminator after finding hundreds of them in a utility room. I have stepped on dozens of them in my clinic in the last month.
I thought they had run their course, but I stepped on yet another cricket yesterday and out popped a horsehair worm, sort of a cricket pinata.
I thought the picture might be interesting to you. When still alive, they tend to “tie themselves in knots”, hence their other nickname, the Gordian worm.
Here are a couple of links with more information, if you’re interested.
http://www.marietta.edu/~biol/field_station/field_notes/horsehair.htm
http://www.ca.uky.edu/entomology/entfacts/ef613.asp
***WARNING***
This is not factual info for anyone reading. Horsehair worms can indeed infect humans and animals and, are incredibly difficult,near impossible to irradicate. Do not take this data as fact.
I don’t know where you got your info, but they are actually correct. They cannot infect humans or pets. They can definitely be ingested, as there have been cases of them being found in human waste or vomit, but they cannot actually parasitize any person or pet. They are actually considered ineffective as a biological control agent (an organism used for pest control) because it can only infect such a small percent of hosts. Maybe you’re thinking of another parasite. Here are some articles if anyone would like to read further, and there are many more available in addition to these.
https://www.kqed.org/science/1937775/these-hairworms-eat-a-cricket-alive-and-control-its-mind
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7471.html#:~:text=Horsehair%20worms%20are%20harmless%20to,tract%2C%20but%20infection%20never%20occurs.