Millipedes are multi-legged organisms, commonly known as “thousand-leggers.” They are arthropods belonging to the subphylum Myriapoda, closely related to centipedes, and are not insects. The factors that attract millipedes are primarily related to their physical requirements and their role as decomposers, drawing them to specific environmental conditions and organic materials.
The Essential Need for High Moisture
The greatest factor attracting millipedes is high moisture. Millipedes require damp environments because their physiology makes them highly susceptible to desiccation. Unlike insects, they lack a waxy, water-resistant layer on their cuticle, causing them to lose body water rapidly through evaporation.
They also lose moisture through their spiracles, the respiratory openings along their body, which they cannot effectively close. This vulnerability means they must constantly seek high humidity to maintain internal water balance. Areas with poor soil drainage, persistent leaks from outdoor faucets or air conditioning units, and excessive watering become attractive magnets. If the environment becomes too dry, these organisms are forced to move in search of more hospitable, moist conditions.
Preferred Outdoor Habitats and Food Sources
Millipedes are primarily detritivores, meaning they feed on dead and decaying organic matter (detritus). This dietary requirement strongly influences their preferred outdoor habitats, which must provide both food and a consistently cool, dark, and damp microclimate.
Highly attractive materials include deep layers of leaf litter, grass clippings, and wood mulch, which retain moisture and offer a continuous food supply. Rotting wood, such as old logs, stumps, or landscape timbers, is a favored location, as it is easily consumed and saturated with moisture. Compost piles and decaying fruits or vegetables also serve as rich food sources. These accumulations of organic debris near a structure create an ideal breeding and feeding environment, as millipedes are actively drawn to the chemical signals released by microbial decomposition.
Why Millipedes Seek Indoor Shelter
Millipedes are strictly outdoor creatures and do not enter structures to find food or establish a colony. Their movement indoors is typically a stress response to environmental extremes in their outdoor habitat.
A sudden shift to drought or excessively hot, dry conditions stresses millipedes, causing them to migrate in search of moisture and cooler temperatures. Conversely, periods of heavy rainfall or localized flooding can displace them, forcing them toward higher, drier ground to avoid drowning.
They often migrate toward the solid foundation of a house as a temporary refuge. Millipedes gain entry through small cracks in the foundation, expansion joints, gaps under doors, or unsealed basement windows while searching for stable, dark, and damp shelter. Once inside, the low humidity of a typical home environment is unsuitable, and they quickly perish from dehydration.