We recently received a query from a reader in London who keeps finding dead creatures on her windowsills and shutters. These creatures look like long black worms, and may be coming into her basement apartment through a gap in the sealant on her window. She has found them to be anywhere from one inch to several inches long. Interestingly, she has never encountered one of these in a living state. She would like to know what these are.

We will start with the great picture she sent us. By using the cotton swab for scale, we can see that the critter is about 2” long. Also, the worm is segmented. To us, it also appears a bit dehydrated.

 

This looks like a typical (though perhaps unhealthy) black worm, or Lumbriculus variegates. The good news is that these worms are not harmful to humans or animals. In fact, they’re commonly sold as food for animals living in freshwater aquariums.

These worms live all over the world, and typically live happily in mud or water (hence one of their other names, the mudworm). At first, it seemed odd that our reader was finding them inside her apartment on her windowsill. However, then we noticed that she had stated that she lives in a basement apartment. She didn’t mention if these little fellows tend to appear more often when it’s been raining outside, but we suspect that they do.

The question is, why would the worms be coming into the house? Our best guess is that they’ve wandered in through the gap in the sealant she mentioned and became lost. This is especially likely if the windowsill tends to accumulate water during rainstorms. Then once the water dries then the worms can’t find their way out again and they dry out.

Interestingly, black worms can become quite dehydrated before actually dying. It is possible that the worms she’s finding are not actually dead, but are slowly dying of dehydration. In nature, the worms would revive during the next rainstorm, but this may not work as well on our reader’s windowsill, especially if they’ve wandered away from the original point of entry.

She can easily remove the critters from her room using a broom or vacuum or by just picking them up and throwing them away. They’re harmless, so there’s no risk in handling them. If our reader wants to give any of the dry blackworms she finds a second lease on life, she can put them outside in wet soil. Any worms that revive will go on to lead a fulfilling blackworm life.

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