ISSUE #19: Hop Aboard the Gooey Train to Gnat Town

Travel in style with one thousand of your closest friends and family.

The end of the year means many of us have been taking or are about to take various modes of transportation to make it to our holiday destinations of choice. Personally, I am about to take a train to my parents’ house, hoping that I don’t get delayed by any errant farm animals along the way. This week, my pre-travel anxiety got me thinking about the kinds of trips bugs take, whether they’re simply meandering through a garden or winging their way across an ocean, as one species of dragonfly does every year. 

There is one bug out there that takes a train whenever they need to move around—or rather, they make a train out of their own bodies. Sciara militaris, a species of dark-winged fungus gnat that lives in central Europe, has a curious way of getting around before it grows wings and is able to fly. In Germany they are called “Heerwurm,” which translates to “army worm,” a name echoed by its Latin taxonomy. 

Sciara militaris is an army “worm” in the same way a rat king is a rat—that is, one thing made up of many things. The worm is actually hundreds, sometimes thousands of tiny wormy larvae all crawling under and around and on top of each other in a long procession. 

Here is a video:

Here is another video of even more of them if you would like to see that: 

In Polish the term for the phenomenon is “pleń,” and though it’s uncommon enough to be called rare, it’s been documented many times. The first recorded mention of pleń comes from 17th century Silesia, a region that now encompasses southern Poland and parts of Germany and the Czech Republic. According to the local custom of the time, a sighting either heralded a coming misfortune or a bountiful harvest. Pick whatever feels right, I guess. 

Four centuries later, and still no one knows exactly why they do it. Part of the problem is it’s difficult to see the before and after. What makes them gather like this? How do they choose a direction? Why travel in a conspicuous group when they’d be stealthier alone? It’s possible that the slow-moving larvae have somehow figured out how to use each other as a sort of moving walkway, traveling faster than they normally could by crawling over the bodies of their brethren, constantly in motion. Wherever they’re going, they’ll get there together.