Millipedes are multi-segmented arthropods that have two pairs of legs on most of their body segments. Most millipedes live outdoors in damp soil and feed on decaying vegetation. Some species defend themselves by producing noxious or irritating fluids that leave stains or cause blisters.
Millipedes that tend to invade structures are usually brown or black and ¼ - 1 inch long. Around structures, they are common under items on the ground, mulch or leaf litter and in heavily thatched turf. Populations build when excess moisture is present, as in excessive irrigation or rainfall. Mass migrations into structures may occur from spring through fall (fall is more common) and may be due to waterlogged soil, mating behavior or overwintering site selection.
Millipedes require so much moisture that they usually die inside structures within hours. Indoor pesticide applications are often not necessary. Use a vacuum to remove mass numbers of millipedes indoors since customers probably don’t want to see them, even if they’re dead. Target pesticide application outdoors around the perimeter of the structure, either with a liquid residual or granular formulation. Mulch and leaf litter should be raked back to expose the ground below. Treating the foundation wall, door thresholds, utility conduits into the structure and other possible entry points with a repellent residual can help reduce the number of millipedes that make it into the structure.