In a fairly long email composed of short, descriptive sentences that were each on their own line, which made the message look like a poem, we were asked about the long, skinny, brown worms that come out after it rains. The reader noted several things about the worms, most notably that they are, once more, long, skinny, and brown, and also that the worms dry out on the sidewalk after the rain evaporates. So, we have a basic “what are the worms that come out after its rain” sort of question, which we have addressed in different contexts a couple of times before. The answer to the reader’s precise question is extremely simple – the long, skinny, brown worms are almost certainly just earthworms – but her email suggests other dimensions of interest, so we’ll discuss why earthworms come out after it rains, and why they often end up dead on the sidewalk when the precipitation and its aftermath have passed.

Earthworms must stay moist or they will perish. (The one pictured above is on the verge of desiccation.) They breathe through their skin, which needs to be sufficiently wet to facilitate the worm’s absorption of oxygen. This is why earthworms generally do not emerge from the ground during the daytime. The soil is cool and wet, but the surface, being exposed to the sun all day, is dry. Thus, if earthworms emerge from the soil at all, they generally do so at night. (Earthworms are called “night crawlers” for a reason.) However, earthworms can also come out while or after it rains, when the ground is of course wet. The precipitation gives the worms a temporary reprieve from their lives underground (not that earthworms necessarily mind being underground, if indeed earthworms can be said to “mind” anything at all).

So the moisture caused by rain, just like the night, is essentially the mechanism or the enabling factor by which earthworms emerge from the soil, but why exactly would an earthworm even want to come to the ground’s surface? A number of factors could play a role, but the primary reason they come up is so that they can move to a different location (with no need to tunnel through the ground). Earthworms also seize their time after it rains on the surface to mate, and this is one of the only times you are likely to see this somewhat unusual process involving the clitellum because copulation generally takes place, as so often seems to be the case, at night. (Earthworms don’t reproduce underground, so they have to surface at night for the act.)

We will conclude by tying up two other topics the reader expressed interest in. The first involves why earthworms die on sidewalks, which has implicitly already been answered: they simply can’t make it back to the soil in time and dry out. They aren’t attracted to the sidewalk in particular – that’s just where they end up, presumably because sidewalks often run along yards, where earthworms live. Our reader was also preoccupied with the length of the worms she found, and all we can say is that earthworms do in fact get quite long. The reader said she found worms as long as a foot, which is definitely long, but not unbelievably so. And with that, we think we have covered all of our reader’s interests and concerns. The long, skinny brown worms are earthworms – which simply are long, skinny, and brown – and people find them on sidewalks because this is where they happen to dry out and die frequently.