Garden millipedes are generally considered nuisance pests rather than destructive garden threats, as they primarily function as decomposers feeding on moist, decaying organic matter. Unlike centipedes, which are predators, millipedes rarely cause significant damage to healthy plants, only occasionally targeting tender seedlings or soft fruits lying on the ground. A large population signals that the outdoor environment is highly favorable for them, often leading to unwanted migration indoors. Millipede control aims to make the surrounding landscape less hospitable through immediate physical removal, environmental modification, and, if necessary, targeted chemical application.
Conditions That Attract Millipedes
Millipedes are highly dependent on moisture and organic debris, indicating a damp, food-rich environment. They thrive in dark, cool, and humid conditions, often found under heavy layers of mulch, leaf litter, or rotting wood, which provides shelter and a steady food supply. Excessive soil moisture from poor drainage or over-irrigation is a primary attractant near the home’s foundation. Leaking exterior water spigots, air conditioning drip lines, or saturated flowerbeds create pockets of perpetual dampness. When outdoor conditions become too dry or too wet, such as during a drought or heavy rain, millipedes migrate in search of more favorable, moist shelter, often ending up inside structures.
Immediate Physical Removal
For an active infestation, immediate physical removal offers the quickest way to reduce the visible population without relying on chemicals. Millipedes are slow-moving, making them relatively easy to collect. A simple and effective method is to use a shop vacuum or a broom and dustpan to sweep up large clusters of the arthropods, especially from patios, sidewalks, or interior areas. If vacuuming, the bag should be sealed immediately and disposed of in an outdoor trash bin, as their bodies can release an unpleasant odor when crushed or disturbed.
Simple traps can also be deployed overnight to capture them in high-traffic areas. This involves laying out damp newspaper, old carpet, or slices of melon or potato; the millipedes will crawl beneath or into these materials seeking moisture and food. The traps can then be collected in the morning and disposed of away from the home.
Long-Term Exclusion and Maintenance
Achieving long-term control relies on making the environment around the home unfavorable for millipede habitation and creating physical barriers. The first step involves correcting external sources of excessive moisture, such as fixing leaky pipes or ensuring that gutters direct water away from the foundation. Watering lawns and garden beds only in the morning allows the surface soil to dry out before nightfall, which reduces the moist conditions millipedes prefer.
Sanitation and landscape modification near the structure are important. Mulch layers should be kept shallow, ideally less than two inches deep, and raked back to create a bare, dry zone of 12 to 18 inches immediately adjacent to the foundation. This dry barrier helps eliminate their primary habitat and food source near the house. Removing ground-level clutter like old boards, stones, firewood piles, and thick accumulations of grass clippings or leaf litter also removes crucial hiding places.
To prevent entry into the home, exclusion focuses on sealing structural access points. Millipedes can enter through small cracks and gaps in the foundation walls, basement windows, and patio slabs. Use caulk to seal visible cracks and crevices in the foundation, paying close attention to utility penetrations where pipes and wires enter the home. Installing tight-fitting door sweeps on all exterior doors, especially at the base of sliding glass doors, will close off a common entry point.
Chemical Control Options
Chemical control should be viewed as a supplementary measure, best used to establish a protective barrier after environmental modifications have been made. Residual perimeter sprays, often containing synthetic pyrethroids like bifenthrin, are applied to the foundation and the ground immediately surrounding it. These liquid insecticides should cover a band extending two to three feet up the wall and three to ten feet out onto the soil to create a lethal zone that migrating millipedes must cross.
For cracks, voids, and other sheltered areas, insecticidal dusts are effective because they remain active longer than liquid sprays, provided they stay dry. Diatomaceous Earth (DE), a non-chemical option, works as a physical barrier; its microscopic, sharp particles abrade the millipede’s outer layer, causing dehydration. Follow the label instructions and ensure the treatment penetrates any remaining organic material to reach the soil where millipedes harbor.