Small Black Worms in Water

A reader asked us a little while ago about some small black worms he is finding on his property. The reader has an air conditioner that drips water onto his carport, which has a crack in it, and small black worms are crawling out of this crack to get to the water. The reader describes the worms as “solid black,” so evidently they don’t have stripes or any other distinguishing body marking. What are these small black worms in the water on the carport?

Like many other questions we receive, we are lacking some crucial details. The creatures are small, but what exactly does that mean? A fairly wide spectrum of sizes could be described as small by different people, making any approximation difficult. We also weren’t told the shape of its body or if it has any appendages. Is it thin or fat? Does it have any legs (or at least prolegs)? Etc. Most of these difficulties would be solved if we had a picture, but unfortunately the reader didn’t send us one. So, we’re not exactly dealing with much information.

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Regardless, we can at least offer a few basic remarks about what our reader is finding, and we’ll start with this: he is very likely finding some type of larva, as opposed to a worm. This sentence (or some variant thereof) is perhaps the most common we write – readers are constantly asking about “worms” that are actually larvae, and this particular case appears no different. (Not that this mistake is unreasonable – larvae look like worms, and in any case it’s not entirely clear what the word “worm” even means.) Why do we think our reader is dealing with larvae? Primarily because of the situation in which he is finding them. Worms, at least as the word is generally understood, live in soil or bodies of water, and while there is a pool of water on the reader’s carport, this still isn’t the type of environment in which you’d expect to find worms. However, it is exactly the type of place in which you’d expect to find various types of insect larvae, many of which, like worms, thrive in moist environments.

We just said “various types of insect larvae,” so clearly we haven’t narrowed the field very much, but in truth it’s extremely hard to do this when we don’t have more information to work with. We thought at first that he might be dealing with one of the many species of black fly larvae, which we have read about in connection with fishing, but it turns out these creatures are only found in running water. He also can’t be finding the larvae of houseflies, a common enough creature to come across in stagnant water, because they are white. (Housefly larvae are maggots.)

Our only other thought is that he is finding black soldier fly larvae (BSFL). The physical characteristics certainly check out – BSFL are solid black and small, under an inch in length – and many people find them around their homes. Our main hesitation in offering this suggestion is that these creatures are normally found in decaying matter (like manure or a compost heap). Unlike, say, maggots, you probably wouldn’t find BSFL in only stagnant water. However, maybe there is some accumulation of organic matter tucked away in the carport (old leaves, for instance), and perhaps this is drawing black soldier flies to lay their eggs here. The pool of water might just be contributing to the habitat, making the leaves moist, and the reader is simply watching the BSFL crawl around their new home.

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Obviously, though, this is speculation, and we aren’t particularly confident in the BSFL hypothesis because we were given such little information to work with. However, we do think it’s highly likely that the black “worms” our reader found are larvae, so even if he isn’t dealing with BSFL, we hope we have pointed him in the correct direction to investigate further.

2 Comments

  1. Kevin Martin

    I have a question! I enjoy swimming in this small lake (large stream?) with my family. While examining some interesting snails, I noticed numerous small, black worm-looking creatures. They appeared to be small- under or around an inch. My sister suspected them to be fish pellets, but my brother and I witnessed them wiggling violently. We believe they might be leeches, as they seemed attracted to us, but we are reluctant to identify it. Can you help us?

  2. Interesting! I had a similar tiny black worm in a bowl near my garden. I didn’t know what it was. Not I’m thinking it was the BSFL!

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