Millipedes are slow-moving, segmented arthropods related to centipedes, but they are not insects. They are primarily outdoor decomposers, feeding on damp and decaying organic matter like leaves and mulch. Millipedes become a nuisance when they migrate in large numbers, often seeking moisture or shelter when their outdoor habitat becomes too wet, such as after heavy rains, or too dry during drought conditions. They are harmless to humans, as they do not bite or sting, but their mass presence on patios and foundations is unwelcome. Effective control focuses on modifying the outdoor environment, creating physical barriers, and applying targeted treatments to manage their populations outside the home.
Modifying the Outdoor Environment
Millipedes require a consistently moist environment and a steady supply of decaying vegetation to survive and reproduce. Therefore, the most effective long-term solution involves eliminating the excessive moisture and food sources near your home’s perimeter. Managing water accumulation often attracts millipedes to the foundation. Ensure that gutters and downspouts are clean and direct all water flow at least three feet away from the foundation to maintain a dry zone.
Fixing leaky outdoor faucets or irrigation heads is another immediate step to reduce localized dampness, as standing water or saturated soil creates an ideal millipede habitat. When watering lawns or garden beds, do so early in the morning so the soil surface has time to dry out completely before nightfall, when millipedes are most active. Proper ventilation in crawl spaces and under decks can also help by reducing the high humidity levels that these organisms seek.
Removing harborage sites is equally important to decrease the available food supply and shelter. Clear away any leaf litter, grass clippings, or other organic debris that has accumulated against the house foundation. If you use mulch in flowerbeds, rake it back so it is no more than two to four inches deep and does not directly touch the structure’s foundation.
Wood piles, planter boxes, stones, and any other items resting directly on the ground near the house should be removed or elevated. Firewood should be stored off the ground and several feet away from the home’s exterior walls to prevent millipedes from using it as a breeding and hiding spot. Keeping the lawn closely mowed and dethatching it regularly promotes air circulation, which helps the soil dry faster and makes the area less suitable for millipede habitation.
Immediate Physical Control and Sealing Entry Points
For immediate reduction of existing millipede populations, physical removal is a straightforward and effective method. Large groups of millipedes found on sidewalks or patios can be swept up with a broom and dustpan or removed using a shop vacuum. The collected millipedes should be disposed of outside in a sealed bag to prevent their return.
Creating a physical barrier around the home’s foundation is a preventive measure that discourages millipede migration indoors. A border of gravel, river stone, or crushed rock, six to twelve inches wide, installed immediately adjacent to the foundation, can serve as a dry zone that millipedes are reluctant to cross. This dry, inorganic material replaces the moist soil and mulch they prefer, making the perimeter less appealing.
Structural integrity is a primary defense against millipedes entering the home. Inspect the foundation thoroughly, paying attention to the ground level where they typically crawl. Seal all visible cracks, crevices, and gaps around utility lines, pipes, and vents with caulk or copper mesh to eliminate entry points.
Ensure that all doors and windows have tight-fitting weather stripping and door sweeps to close off the small gaps at the base of thresholds. Even small openings can allow millipedes to crawl through, particularly during mass migration events. Maintaining these seals is a continuous task, as weather stripping can deteriorate over time, creating new access routes for these crawling arthropods.
Utilizing Targeted Treatment Methods
When environmental modifications and physical exclusion are insufficient to manage a large outdoor population, targeted treatments can be applied to create a chemical barrier. One natural option is Diatomaceous Earth (DE), a fine powder made from fossilized diatoms. DE works by absorbing the waxy outer layer of the millipede’s exoskeleton, leading to dehydration and death.
This powder should be applied as a light, visible dusting to dry areas around the foundation, in planters, and along known migration paths. Because moisture neutralizes its effectiveness, DE must be reapplied after rain or heavy watering. Boric acid dust is another option, which can be puffed into cracks and voids where millipedes hide, providing a long-lasting residual.
For a more aggressive approach, use liquid or granular insecticides labeled for millipede control, often containing pyrethroids like bifenthrin or cyfluthrin. The most common application is a perimeter barrier treatment, where a band of insecticide is sprayed or spread three feet up the exterior wall and three feet out onto the ground from the foundation. This barrier intercepts millipedes as they attempt to cross from the yard to the structure.
Granular formulations are beneficial in mulched areas or turf, as they release the active ingredient slowly and are less affected by light rain than liquid sprays. Apply granular products using a spreader and water them in lightly, according to the product label, to activate the insecticide.