A reader from San Antonio, Texas wrote to us about worms with bioluminescence that he has been finding around his home. He hasn’t found the bioluminescent worms very often – just on a few evenings, and only during the winter months. When a worm exhibits bioluminescence, this means that its body is producing and emitting light though a chemical reaction – in other words, a bioluminescent worm is a worm that glows. So, in short, our reader is finding some sort of glowing worm. There are a number of so-called “glowworms” (also spelled “glow worms”), and of course all of these worms (which are actually not worms, but insect larvae) exhibit bioluminescence. Our reader was curious what kind of glowing worm he found, and it might seem obvious that he found some type of glowworm, but it’s a little more complicated than that. Below we’ll explain what glowworms are, and in so doing we’ll try to help our reader with his question about the bioluminescent worm he found.

To begin, glowworms, as mentioned above, are not worms, but rather insect (more precisely, fly and beetle) larvae. (Actually, glowworms can be either a larva, an immature form of an insect, or a larviform female, which is an adult form of a species, even though it resembles a larva.) As larvae, glowworms are worm-like in body form and movement, but they aren’t actually worms. “Glowworms” is an informal and common name given to various kinds of larvae, so the term refers not to the larval form of any particular species of insect, but rather to many species that are members of the order Coleoptera. Perhaps the most well-known glowworms belong to the family Lampyridae, the members of which are more commonly known as “fireflies.” There are around 2,000 species in this family, and they are all marked by their use of bioluminescence to attract prey or mates. Since glowworms are the larvae of flies and beetles, they are rather small, or any case they are almost certainly smaller than the creature our reader found, which he estimated to be about three inches in length.

So, if our reader didn’t find a glowworm, what did he find? We can’t be entirely sure, but assuming he did in fact find some type of worm (as opposed to a larva), we would guess that he found some type of earthworm. Glowworms are far from the only creatures in nature that exhibit bioluminescence. Lots of other insects do (not just glowworms and the adult forms they grow into), as do arachnids and annelids, the latter of which is the phylum that earthworms fall under. (As an interesting side note, even some types of fungi are bioluminescent.) There are actually several different types of earthworms that display bioluminescent abilities; indeed, three out of the 16 families that make up the subclass Oligochaeta (to which earthworms belong) contain species that are bioluminescent.

Unfortunately, this is as far as we are able to help our reader with the information we have. We don’t know exactly what species of bioluminescent earthworm our reader might have found, if he found a type of bioluminescent earthworm at all. (Maybe he did find a type of glowworm and simply overestimated its size.) The reader mentioned that only a small portion of the worm he found was bioluminescent, which isn’t unusual (the entire bodies of bioluminescent creatures don’t necessarily, or even commonly, glow), but alas, without more information or a picture, this physical trait alone isn’t enough to determine more definitively what species he might have found. In any case, we’re pretty confident he found a bioluminescent earthworm, and hopefully that satisfies our reader’s curiosity or helps him on his quest to discover the precise species he found.