A reader wrote to us a while ago about a worm that can “stand up on end and bite or bore into” skin. The worm is about a quarter of an inch long and moves like an inchworm, which is in fact a type of caterpillar, but then once it is ready to bite, “it raises up on end and tries to worm its way into the skin.” The reader has a young daughter who loves to play outside, so he is keen to find out what the biting worms may be. He hasn’t been able to take a picture of the worms that bite, nor has he been able to find out any information about them. What might these biting worms be?
Without a picture, it’s very difficult to even narrow down the possible options. Moreover, the reader seems to only speculate that the worm bites or “bores into” skin – neither he nor his daughter was actually bitten, at least as far as his email suggests. So, it is hard to know if the “biting worm” even bites, and we don’t even know if it’s a worm. In fact, we would say more likely than not it isn’t a worm, as the types of worms one would see walking around outside (like the various species of earthworm) don’t bite. We suspect the reader found some sort of caterpillar, which in general aren’t harmful, although several species can sting with their setea if they are touched. We are told the creature moves like an inchworm, so, in the absence of any other evidence, we’ll assume the caterpillar our reader found is an inchworm, the larval form of geometer moths, of which there are tens of thousands of species. Although many inchworms are actually about an inch long, certainly not all of them are, and in any case inchworms grow throughout their lives, meaning they can be quite small when they first hatch. So, the fact that what the reader found is only a quarter of an inch long doesn’t mean it isn’t an inchworm. Also, that the creature our reader found can stand up suggests it’s an inchworm too – inchworm movement is not limited to inching along the ground – although several other caterpillars can stand up this way as well.
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Although some people have reported being bitten by inchworms, which evidently feels like a mosquito bite, this seems to be rare, and it might even be impossible if the creature is only a quarter of an inch long, as its mouth would presumably not be big enough to grab onto skin. Inchworms are also a favorite of children, who often pick them up, let them crawl on them, and keep them as “pets.” In addition, inchworms’ primary defense mechanism is to spin webs, as opposed to bite predators. When threatened, some species will repel themselves from leaves on a thread. They will wait out the threat, and then once the thread hardens, they climb back up. Again, there are tens of thousands of species of geometer moths, and the larval form of each doesn’t necessarily act in exactly the same way, but inchworms are not known for biting. And no matter what, we don’t think our reader found anything that will bore itself into a human body. The only creature we have heard of that screws itself into a human body are the appropriately named screwworms, but these have been eradicated from much of the world and they only attack open wounds.
We aren’t certain our reader found inchworms, but it is the most plausible suggestion we can put forward on the basis of the available information. If he did find an inchworm, we don’t think he should be worried. The fact that the inchworm stood up is part of its regular movement, and perhaps the reader merely misinterpreted this as a threat. As always, though, it is good to exercise caution when dealing with unknown creatures, and in general it’s probably best to leave them alone. If you don’t bother them, they probably won’t bother you.
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