Moth Flies: Yet Another Incorrectly Named Arthropod

Shoutout to Andy Reago and Chrissy McClarren for posting this cute little fella on Flickr!

The bathroom in my freshman dorm was infested with moth flies. They rarely if ever appeared in the sinks or stalls, thank goodness, but they were all over the showers. Some days it was bad enough that I would open a shower curtain, say “nope,” and move on to the next one. On really bad days, I would check out several showers and end up having to pick whichever one had the least amount of flies. Apparently these guys are a sign of standing water somewhere in the drainage system, so let’s just say I’m glad I don’t live in that building anymore and I hope they get that fixed.

Moth flies, drain flies, sewer flies, sink flies… whatever you’ve been calling them is wrong, because they’re actually gnats. They’re in the order Diptera like flies, but they are gnats all the same, so I’m going to call the puddle gnats. Puddle gnat larvae live in whatever nasty film has developed in their standing water habitat, usually in places like compost piles or the dirty pipes my dorm building had, and make use of a special tube they stick out of the film like a snorkel to breathe through. The larvae are detritivores that eat the algae and decaying gunk in their habitat. They may have gross meal preferences like flies, but they don’t bite and, unlike their partial namesake, they don’t spread disease. In that sense they’re not too bad to have around for their cleaning efforts – except that their presence indicates that you’ve got some gross water somewhere, of course.

After growing for one to two weeks, puddle gnat larvae pupate and emerge as adult puddle gnats within a day or two. The adults also only live for a couple weeks, but these insects breed and multiply pretty quickly. Being relatively clean insects (surprisingly enough), the only reason puddle gnats become a problem is simply because people don’t want them around – I mean, I love arthropods, but I certainly didn’t like having them in my shower. Fortunately, if you clean up whatever grossness the puddle gnat larvae have been feeding on, the infestation will take care of itself. Literally – moth fly larvae become cannibals when their regular food source goes away.

Despite their grimy choice in food and habitat, puddle gnats are actually super cute up close. I didn’t really notice this in the shower because I was too busy trying to avoid them, but I ran into some puddle gnats in the laundry room this year and was able to get a better look at them. They really do look like miniature moths, with fluffy antennae and bodies and shiny fly wings laced with fuzz. I mean, just look at the picture at the top of this post! They’re the cutest little dipterans I’ve ever seen! As fancy as their wings are, however, puddle gnats aren’t the best fliers and actually prefer to crawl if they can. They spend their days basking on walls and other flat surfaces, but do enjoy flitting around lights or their yucky water at night.

You know, I never thought I would say that I like those weird little bugs taking up space in the shower, but I’ve gained a new appreciation for them after learning about their pipe-cleaning behaviors and adorable anatomy. I still don’t want them in my shower, but the next time I see moth flies chilling around some gross-looking puddle on a hiking trail, I’ll be sure to give them a nod for their efforts in keeping the forest clean.

Somebody’s got to deal with that nasty water; it might as well be cute little puddle gnats.

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