By Jim White, Associate Director, Land and Biodiversity
I have always enjoyed answering questions about wildlife and take a bit of pride in being able to come up with answers quickly. However, every now and then there are questions that are real stumpers. These questions are always the most fun to work on and often require communication with other naturalists, flipping through old field guides, and of course searching the web.
One such question turned up the other day. A friend of mine called me when he and a few of his neighbors discovered an interesting scene on the neighborhood sidewalk. My friend described it as several groups of worm-like things forming a rope and walking en masse in a clockwise circle. The ropes were several “worms” thick and joined head to tail. He was speculating (in jest) that they were an alien life form. To be honest I was wondering if he might be right. Luckily, one of the neighbors, Paul Dreyfus had a digital camera and was able to take a few photos and send them to me. I waited in anticipation, figuring that once I saw the photos I would know exactly what the “worms” were. But noooooo! Although I could tell that they were insect larva I had no idea what kind.
I decided to ask Richard Smith a well-versed entomologist that I know. He was also stumped but did some web searching of his own and found our answer in a photo on an obscure garden listserve. Sure enough the photo was a match – the “aliens” were the larvae of a species of Dark-winged Fungus Gnats (family Sciaridae). As their common name implies, the larvae of these small flies (order Diptera) feed on fungus, but they also eat the root hairs of many plants. Some species are known pests of mushroom cultivation and greenhouse operations.
So with the identification in hand I set out to find out all I could about these intriguing insects. I figured a few minutes on the web would give me as much information as I wanted on the little guys. Wrong again. So far I have only found out the following:
• The larvae often live in large congregations and from time to time move en masse to new locations.
• In Europe there are several species of Dark-winged Fungus Gnats, especially the army worm Sciara militaris, that migrate in processions up to ten meters long, containing thousands of individuals.
• The circles apparently form when the leading larvae mistakenly hooks up with the larvae at the tail of the “rope”, forming an endless loop.
Many questions remain about why and where the larval migrations occur and how frequently the circles form. I will keep searching for these answers and report my findings (if any) in another blog. Meanwhile, please contact me if you’ve seen, or have additional information about, these “alien worm circles”.