Millipedes thrive in moist environments and are most commonly found outdoors in soil, mulch, and decaying organic matter. They feed on decomposing plant material and are an important part of the natural ecosystem. 

Their movement indoors is usually driven by environmental changes rather than a desire to infest structures. During periods of heavy rain, flooding, or sudden shifts in temperature, millipedes may migrate in large numbers, seeking shelter in drier areas. This often leads to sudden indoor sightings, particularly in basements, garages, and ground-level rooms. 

Homeowners commonly notice millipedes along baseboards, near entry points, or clustered in damp areas. In some cases, large numbers may accumulate near doors or windows after weather events. Because they do not survive well indoors, many will die shortly after entering, which can lead to repeated sightings of dead or dying millipedes.  

Millipedes do not bite, sting, or cause structural damage. However, they can release a mild defensive fluid when disturbed, which may have an unpleasant odor and, in rare cases, cause minor skin irritation. While they are harmless, their presence is often a strong indicator of excess moisture, poor drainage, or environmental conditions around the structure that are attracting them. Effective control focuses on reducing moisture, improving drainage, and sealing entry points to prevent large numbers from entering.