Millipedes are important recyclers that break down decaying plant matter as they feed (Figure 1). They accumulate in areas where there is moisture coupled with mulch, fallen leaves, or a significant thatch layer.
During some times of the year, large numbers of millipedes can appear suddenly, covering sidewalks and sides of buildings. Reasons for this behavior are not clear, but the two main thoughts regarding this activity are that it may be due to:
1) Seasonal dispersal from overwintering sites in fallen logs and other shelters to open grassy sites, and/or
2) Searching for mates.
General Millipede Management Tips
Minimize Moisture and Hiding Places
The most effective, long-term measure for reducing entry of millipedes (and many other pests) is to minimize moisture and hiding places near foundations.
- Remove leaves, grass clippings, heavy accumulations of mulch, boards, stones, boxes, and similar items lying beside foundations. These sites attract and harbor pests. Items that cannot be removed should be raised off the ground, if practical.
- Manage moisture when possible. Do not allow excess water to accumulate near foundations or in crawl spaces. Divert moisture with properly functioning gutters, down spouts, air conditioner drain tubes, and splash blocks. Homes with chronic drainage problems may need to have tiles or drains installed or the ground sloped so that surface water drains away from the building.
- Reduce humidity in crawl spaces and basements by providing adequate ventilation, sump pumps, polyethylene soil covers, etc.
- Millipedes can thrive in the moist, dense thatch layer of poorly maintained turf; de-thatching the lawn and keeping grass mowed close should make areas less suitable for millipedes.
- Over-watering contributes to millipede problems. Adjust lawn sprinklers and irrigation systems to eliminate puddles.
Seal Entry Points
- Seal cracks and openings in outside foundation walls, around the bottoms of doors, and around basement windows. Install tight-fitting door sweeps or thresholds at the base of all exterior entry doors. Apply caulk along the bottom outside edge and sides of door thresholds. Seal expansion joints where outdoor patios, sunrooms and sidewalks that abut foundations. Expansion joints and gaps should also be sealed along the bottom of basement walls on the interior to reduce entry of pests and moisture from outdoors.
- Wandering millipedes that end up in kitchens, living rooms, etc. soon die from a lack of moisture. Sweep or vacuum them up and discard.
- Insecticides may help to reduce inward invasion of these and other pests when applied outdoors, along the bottom of exterior doors, around crawl space entrances, foundation vents, utility openings, and underneath siding.
- It may be useful to apply a barrier insecticide treatment along the ground beside foundations and a few feet up the base of foundation walls. Rake back heavy accumulations of mulch and leaf litter before treatment. Application of insecticides along baseboards and other interior living areas of the home rarely are effective in controlling millipedes.
- Various insecticides sold in hardware/lawn and garden shops are effective, including Sevin and synthetic pyrethroids (e.g., Spectracide Bug Stop, Ortho Home Defense System). 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 the foundation.
- Read and follow all label instructions.
By Lee Townsend, and Mike Potter, Extension Entomologists