What are those small worms that appear in the thousands after it rains? The worms are about an inch long, they smell, and they prevent me from walking where I need to go, so I how do I get rid of them? This is, paraphrased, the question of a frustrated reader, wondering why rain causes an army of small worms to appear on her driveway after it rains.

Let’s begin with what these worms might be. As most people who have walked outside after a rainstorm know, there are often tons of worms on the sidewalk, street, and driveway. Why does this occur? Since worms are susceptible to drying out, which inhibits their ability to breath, they normally come out of ground only at night (you know, when that massive, burning-hot orb isn’t out). That’s why we call earthworms “nightcrawlers.” However, when it rains during the day, worms can come out – often for mating purposes – because the ground is wet, and hence they are not as susceptible to desiccation. They are basically seizing a rare moment for daytime sex.

So, it’s a widely observed phenomenon that worms come out of the ground when it rains, and there is a fairly straightforward reason for this occurring. But this may not address our reader’s question because, one, she emphasized that the worms are small (often an inch long or shorter), two, she said that they smell, and three, she said that this hasn’t occurred before.

Unfortunately, without more information, it’s really difficult to be sure what sort of worm or worm-like creature this reader is dealing with. The earthworms that come out after it rains are very often larger than an inch (indeed, they can be several inches long), and in our experience, the worms generally don’t carry any particular odor (although this is possible). In fact, it often smells very good after it rains for reasons that don’t concern us presently.

Of course, other types of worms can emerge from the ground after it rains – for example, you can often find potworms in your garden or compost after it rains – but it would be slightly strange to see these worms, let alone thousands of them, exclusively on your driveway after a rain storm.

It’s also possible that our reader is dealing with a particularly large amount of millipedes or centipedes. People have reported these creatures coming out in droves before, and they can be quite a problem, especially if they migrate into your garage or house.

Finally, it’s entirely possible that what she is seeing aren’t worms at all – this particular reader doesn’t make mention of them moving, for example – and it could be that what she is seeing is the seed or other castings from a nearby tree, which would explain the unusual observation of them having a smell.