Millipedes play an important role in breaking down decaying plant matter. These multi-legged arthropods accumulate where there is some moisture coupled with mulch, fallen leaves, or a significant thatch layer.
Large numbers of millipedes can appear suddenly to cover sidewalks, porches, and sides of buildings. Reasons for their activity are not clear but two main thoughts are:
1) It is their seasonal dispersal from overwintering sites in fallen logs and other shelters to grassy sites, and / or
2) They are searching for mates.
Millipedes are most problematic around homes near or in woods or those with extensive naturalized areas around foundations. Millipedes can be so abundant in these situations that there is no effective response other than waiting for their activity to end.
Minimize/Eliminate Hiding Places
The most effective, long-term measure to reduce nuisance millipedes (and many other pests) is to minimize humid shelters, especially along foundations.
- Remove accumulated leaves, tall grass, piles of firewood, etc. along foundations. These items often attract and harbor pests. Items that cannot be removed should be elevated to allow air circulation and drying.
- Divert water from the foundation wall with properly functioning gutters, down spouts, and splash blocks. Leaking faucets, water pipes, and air conditioning units should be repaired. Lawn sprinklers should be adjusted to minimize puddling. Excess rainfall or overwatering also may contribute to millipede problems.
Various lawn and garden insecticides containing synthetic pyrethroids (e.g., bifenthrin, cyfluthrin, Deltamethrin, or permethrin) may provide some control outdoors, but the hard exoskeleton of these creatures protects them, leading to uneven results. Treatment can be accomplished with a compressed air “pump-up” or hose-end sprayer. Dust formulations (e.g., silica get, diatomaceous earth) also work well for treating cracks, weep holes, and similar openings in foundations.
Application of insecticides indoors is of little use in controlling millipedes. Most wandering millipedes that venture indoors soon die from a lack of moisture. Sweep and discard them, as needed.
By Lee Townsend, Extension Entomologist