Millipedes are arthropods belonging to the class Diplopoda, characterized by their elongated, segmented bodies, with most segments featuring two pairs of legs. Despite their common name translating to “thousand feet,” most species have far fewer limbs. These slow-moving creatures are primarily detritivores, meaning they feed on decaying plant matter. This makes them beneficial recyclers in most ecosystems. For people, pets, and plants, millipedes pose a negligible threat and are only a nuisance when they congregate in large numbers or wander indoors.
Millipede Threat Levels to Humans and Pets
Millipedes are not aggressive and lack the ability to bite or sting, separating them from their relatives, the centipedes. Their primary defense mechanism is passive, involving coiling their bodies into a tight spiral to protect their vulnerable undersides. When threatened, many species will secrete an irritating fluid from glands along their body segments.
This defensive secretion is a mix of chemicals, most commonly benzoquinones, but can also include small amounts of hydrogen cyanide, hydrochloric acid, or phenols. While not dangerous to humans, direct contact can result in temporary skin discoloration (often a brown stain) and localized irritation or burning. This is especially true if transferred to sensitive areas like the eyes. Washing the affected area with soap and water is the standard treatment.
Pets, particularly dogs and cats that mouth or ingest a millipede, may react to these defensive fluids. The ingested chemicals can cause mild gastrointestinal upset, resulting in symptoms like drooling, vomiting, or general discomfort. Serious or lasting harm is uncommon, but observation is suggested. A veterinarian should be consulted if symptoms persist or are severe.
Damage to Plants and Property
Millipedes perform an important ecological function as decomposers, breaking down leaf litter, decaying wood, and other dead organic matter. This releases nutrients back into the soil. Their diet makes them beneficial in a garden setting, enhancing soil fertility and aeration. They are often found in dark, moist environments like under mulch, stones, or rotting logs.
Damage to live, healthy plants is relatively rare because millipedes prefer soft, decaying material. However, if populations are high or if environmental conditions, such as drought, force them to seek moisture, they may occasionally feed on tender plant parts. This feeding usually targets soft fruits, roots, or the leaves of seedlings that are in contact with the ground.
Millipedes are not considered a threat to sound structural property, as they do not consume dry wood or building materials. They may be found in areas with water damage or high moisture, such as damp basements or crawl spaces. However, they are only consuming the already decaying material. Their presence in these areas points toward a moisture problem rather than a structural infestation.
Keeping Millipedes Out of the House
Millipedes are highly dependent on moisture and typically only migrate indoors when their outdoor habitats become too dry (during a drought) or too waterlogged (after heavy rain). Once inside, they are usually found on the lowest level of the home, such as basements or garages. They often die quickly due to the lack of sufficient moisture.
The most effective method for managing their indoor presence is to focus on exclusion and environmental modification. Sealing potential entry points is a useful first step, involving applying caulk to cracks and openings in the foundation, around utility pipes, and along the edges of doors and windows. Installing door sweeps on exterior doors can also close the gap between the door and the threshold.
Outdoors, excess moisture and organic debris near the home’s foundation should be eliminated to make the area less appealing. This includes removing leaf litter, grass clippings, and woodpiles close to the house. Replacing organic mulch next to the foundation with a 6-to-12-inch border of gravel can help improve drainage and reduce the damp habitat they seek. If millipedes are found inside, they can be swept up or vacuumed and then disposed of, as they do not reproduce indoors.