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 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.