Millipede Migration

Yesterday afternoon, while hiking at South Platte Park, I encountered hundreds of small millipedes crossing the paved bikeway.  Worm-shaped and close to an inch long, some had been accidentally crushed by passing walkers and cyclists.

This mass exodus was taking place one day after a six-inch snowfall blanketed the region; as the snow melted in the bright Colorado sun, saturated soil may have triggered their movement.  On the other hand, millipede migration is known to occur in autumn as these abundant invertebrates seek new food sources (decaying plant and animal matter) and search for wintering sites.

Primarily nocturnal, most terrestrial invertebrates are seldom encountered during the warmer months unless one is an active gardener.  While most insects overwinter as eggs or pupae, pillbugs and millipedes are among those invertebrates that may live for many years; when threatened by cold weather, most seek shelter beneath leaf litter or in loose soil but some escape to basements and garages, a choice not generally appreciated by homeowners.