We received a question from a reader recently who has been finding red worms in his sink drain. The reader describes his situation well, so we’ll quote (with a few minor edits) his entire email, after which we’ll get on to the task of identifying the worms in the drain: “These worms keep entering through the sink hole of my bathroom. I just pour water and wash them down the drain again. But still they manage to come up again. They crawl really slowly and they move away from the sink hole. I am scared that they might be harmful because their color is very red…..like blood sucking parasites! Please help. Let me know what these are and how you can get rid of them. Even if they aren’t harmful, I’ll be happy not to see them again.”

When we first read this question, we were hung up on the “sink hole” part. Why is the reader worrying about a few worms, we thought, when he has a sinkhole, those gaping pits that can envelop entire buildings, in his bathroom? However, upon a moment’s reflection, we realized he just meant the drain of a sink, which is probably why he used “sink hole” (two words) and not “sinkhole,” with the latter denoting the chasms that periodically open up due to a surface layer collapse. But we digress.

In almost all cases involving “worms” in a drain, we immediately suggest that whoever wrote to us found moth fly larvae, one of the most common creatures we write about. Moth fly larvae are, of course, the larval form of moth flies. They are quite small – generally, they aren’t much larger than a quarter of an inch (half a centimeter) in length – and they are so often found in drains that the adults are commonly called “drain flies.” The adults lay eggs in the decaying organic matter that accumulates in drains, and then the larvae hatch about 48 hours later, growing up in the filth that accumulates in all drains.

Simply washing them down the drain, even if this is done with boiling water and bleach, will have basically no impact on the infestation, as this won’t remove the conditions (i.e., the organic film that lines drains) that gave rise to the problem in the first place. Instead, you need to physically scrub the drain with a brush and drain cleaner to eradicate the problem. You might also need to use a plumber’s snake to remove any clogs, as these are often responsible for the buildup of organic matter in drains. We have written about getting rid of moth fly larvae many times before – recently the topic came up in connection with moth fly larvae in the toilet, for example – so our reader can search the site for more information, or perhaps to find comfort in the fact that so many other people have had similar problems with their drains. There are also some really excellent sites on moth fly larvae control, like the guide published by the University of California Integrated Pest Management Program, that can be found elsewhere online.

However, we aren’t actually sure our reader found moth fly larvae, even though this seems like such a promising suggestion. The main thing that calls our suggestion into question is that the larvae are “very red,” and moth fly larvae are not naturally red. Apart from some species of caterpillars, which wouldn’t be found in a drain, we only know of one type of larva that can be red, and that is the midge fly larva. Due to the presence of hemoglobin, some midge fly larvae are a vibrant red color, and hence they are periodically referred to as “bloodworms.” These creatures aren’t generally associated with drains – certainly not to the extent that moth fly larvae are – but bloodworms are found in a broad range of aquatic and semiaquatic habitats, so a drain definitely isn’t a strange, much less impossible, place to find one. Not much is written about removing midge fly larvae from drains in the house, but the advice we supply above in connection with moth fly larvae is almost certainly applicable to a midge fly larvae infestation as well.

So, we think our reader found either moth fly larvae or midge fly larvae, and both suggestions have supporting evidence. Moth fly larvae are definitely the more common pest in drains, and they are almost always the “worms” in the drain that people find. However, they aren’t red, although we suppose they could become this color if there is something red in the drain that is coloring their body. This isn’t inconceivable, but if the larvae are truly “very red,” as our reader reports, then we suppose it is more likely he found midge fly larvae, even though these aren’t a common pest found in drains, at least in our experience.

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