“Alien Worm Circles”

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.

Strange insect larvae walking in a circle on a sidewalk.  Photo by Paul Dreyfus.
Strange insect larvae walking in a circle on a sidewalk. Photo by Paul Dreyfus.

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.

Dark-winged Fungus Gnats close-up.  Photo by Paul Dreyfus.
Dark-winged Fungus Gnats close-up. Photo by Paul Dreyfus.

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”.

162 thoughts on ““Alien Worm Circles””

  1. The larvae of the Dark-winged Fungus Gnat can be a problem in greenhouses and some other indoor plant collections. If the soil is very moist in potted plants the larvae can eat the roots especially of young plants. There is also some indication that the larvae can spread root fungus in plant collections, The adult gnats can be a nuisance, however do not cause plant damage. The Dark-winged Fungus Gnat rarely causes damage to outside plants.

  2. Debbie Langer

    Oh my gosh. I had these in my driveway and had no idea what they were. My son came across this post and, lo and behold, they are exactly what I found. There were several “lines” of them and one circle. I have pictures, but I took them after I stayed bug killer on them. Oh, well. I live in Pasadena, MD.

  3. I had one of these perfectly round rope looking species at my front door. It appeared to be a braided bracelet but then saw movement. It freaked me out. Our area has had excessive rains & wondered if that was why we saw it appear.

  4. I saw one of these rings recently on a stepping stone in my yard after a rainstorm, and it did look like a bracelet at first–very strange to watch! I checked a half hour later and they were gone. I’m in Howard County Maryland.

  5. Ginger Hepler

    I woke to find several moving masses of these this morning, but even more scary, two circles- right next to each other-each about 8 inches across. I took a picture before scooping them up and disposing of them. I also bleached the whole area. Here’s my thoughts: about six weeks ago I had my entire front yard scraped down and rebuilt with fresh Kentucky Blue Grass sod. We also installed an underground water sprinkler system. I’ve been watering a lot, so the mention in the article that it could be from the insect who love moist fungal conditions could be entirely correct.

  6. Wow Jane. I’m in Oakdale, MN and I just went to take out the trash and found a ring on my walkway. I thought my kiddos drew something. Nope! When I saw it all moving in the light I felt that icky creepy crawly feeling LOL. Oddly, We have a beehive of “bumble bees” under our front steps near the circle.

  7. We live in Nazareth Pennsylvania and we had a ring as described by all of you of moving little critters in a circle they kept going round and round we did not kill them because we found them to be interesting. We googled and tried to find a source but were unsuccessful so we just let them be The next day they were gone. It’s nice to finally have some kind of answer to what they were.

  8. Just had a ring of these on my patio walkway yesterday! We’re in WNY, outside of Buffalo. No recent rain here that would explain yesterdays sighting. I’m normally very insect friendly and let mother nature do her thing, but these alien creatures had to be disappeared of! I have video if it is something that can be of benefit to tracking where these rooms are being seen. We were thinking of possibly reporting to DEC in case they were some kind of non native invasive species.

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