By Brianna Nugent, Community Science Program Manager
Animals migrate to search for food, water or breeding grounds, and iconic species like sandhill cranes and monarch butterflies are familiar. However, the mini migrations that take place on the ground at night during spring, late summer and fall are lesser known. For reasons that are still not completely understood, millipedes have been observed traveling in groups by the thousands under the cover of darkness — something I witnessed for the first time recently.
A Sci-fi Moment
I assist with bird banding field trips in the fall at Chadron State Park, and a couple years ago, on my first night staying in one of the cozy rustic cabins, I went outside to sit and enjoy the evening. It was a clear night with a slight chill in the air, and as darkness fell, a heavy blanket of deep blue studded with shimmering stars covered the sky. But — as my luck would have it — I couldn’t just have this peaceful night play out like I had envisioned. While attempting to grab something from inside the cabin, I discovered that I had been locked out and my key was sitting on the table. As I was trying to figure out a game plan, I made another discovery: Hundreds of tiny millipedes began marching across the porch, making their way straight for my front door. It looked like a scene from a sci-fi movie.
I eventually got back into the cabin through an open window and found that they had gotten inside. I ended up covering the small space under the door with a towel, and by morning, the porch was completely void of marching millipedes. I released the few that managed to get inside the cabin.
This bizarre phenomenon sparked a series of questions that sucked me into an internet rabbit hole on all things related to mass millipede movements.
What Triggers Millipede Migrations?
Millipedes are long, cylindrical or flat invertebrates that are closely related to lobsters and crayfish. Their name translates to “thousands of feet,” despite most species having less than a hundred legs. Millipedes are harmless to humans and spend their time in moist soils under logs and leaf litter, breaking down organic matter and improving soil health. Since they are typically nocturnal with their active window falling between dusk and dawn, you may have never seen one.
Researchers still have a lot to learn about millipedes and their behaviors, but it is believed that certain factors may trigger these migrations. Excessive rain or extreme droughts, breeding seasons, resource competition or habitat disruption are all potential factors that could cause these spikes in movement. As the fall chill begins to set in during September and October, millipedes may be seeking out quarters to hibernate and overwinter, leading to increases of these nightly migrations.
Tips for Keeping Them Out
While I love finding millipedes, I don’t necessarily want droves of them in my home. If you’ve had millipede home invasions, look for entry points, such as underneath doors or other small openings, and avoid using insecticides as they are virtually ineffective in this scenario.
Instead, install weather strips under garage doors to keep millipedes and other insects from seeking shelter in your space.
Also, organic matter that stays moist and can provide shelter, such as leaf litter and mulch, should be moved away from your foundation to deter millipedes from establishing around your home.
