Common Name: Millipede
Scientific Name: Various
Millipedes are sometimes called “thousand-leggers,” but they usually have 30-90+ pairs of legs. They are widely distributed throughout the United States and most of the world, with about 1,000 species occurring in the U.S.
Adults about 1/16-4 1/2″ (2-115 mm), usually cylindrical and wormlike but some slightly flattened. Color usually blackish or brownish but some red, orange, or with mottled patterns. With 1 pair short, 7-segmented antennae. Usually a cluster of simple eyes (ocelli) on each side of head.
Most body segments bear 2 pairs of legs, except first 3-4 segments and last 1-3 segments which have 1 pair or no legs. First instar millipedes usually have no more than 7 body segments and 3 pairs of legs. Additional segments and pairs of legs are added with each molt.
(1) Centipedes (class Chilopoda) with flattened body, have 1 pair of legs per body segment, antennae with 14 or more segments.
(2) Pillbugs and sowbugs (order Isopoda) with 7 pairs of legs.
Millipedes overwinter as adults or young. Adult females lay 20-300 eggs, either in soil cavities or among decaying organic matter during the summer; however, they can breed year round under tropical conditions. Eggs hatch after several weeks. In most species, there are from 7-10 molts. In many species sexual maturity is not reached until the second year, others require 4-5 years. They eat their molted skins to restore lost supplies of calcium. Adults often live for several years.
Members of several millipede groups give off an ill-smelling, repugnant fluid through openings along the sides of the body. In some species, this fluid contains hydrocyanic acid, iodine, and quinone which is toxic to some arthropods and small animals. It can cause vesicular dermatitis (small blisters) in humans.
Millipedes have high moisture needs, like pillbugs and sowbugs. They are typically found in areas of high moisture and decaying vegetation such as under trash, piles of grass clippings, flower-bed mulches, leaf litter, etc. Millipedes are nocturnal or active at night. Sometimes, and usually in the autumn, millipedes will migrate in great numbers. This is thought to be the result of natural hibernation movement, heavy rains and a rising water table forcing them out of their natural abodes, warm temperatures in late autumn, their apparent habit of crawling up such things as trees and walls for mating purposes and/or extremely high populations building up under very favorable conditions, followed by drought. This can involve several hundred individuals to hundreds of thousands, sometimes several million millipedes.
They usually do not survive indoors for more than a few days unless there are high moisture conditions and a food supply present. Millipedes are primarily scavengers and feed on decaying organic matter, usually plant material but occasionally on dead insects, earthworms, and snails. They may attack living plants during dry periods in order to obtain needed moisture.
The key to controlling millipedes is to reduce or eliminate the moist areas which make their survival possible. Outdoors, 4 things should be done.
(1) Dethatch the lawn because dense thatch just above the soil surface holds moisture.
(2) Mow the lawn closely and edge it because this promotes quicker drying.
(3) Remove debris such as accumulation of leaves and wood debris, rocks, heavy mulch, store firewood, etc. up off the ground, and provide adequate ventilation in crawl spaces to reduce sheltered, damp hiding places.
(4) Water lawns in the early morning to allow the grass to dry during the day. Application of appropriately labeled residuals can be made to building foundation walls, perimeter flower and/or ornamental plant beds, unfinished basements, and crawl spaces. Wettable powder and micro encapsulated formulations are best, but dusts are also good in drier crawl spaces.
During mass migrations, residual pesticide deposits will have little effect because of the short exposure time to them. If the major population can be found (may require a night-time inspection), such as in outlying grassy or wooded areas, these should be treated during the day with an appropriately labeled contact insecticide. Otherwise, night-time treatment of the millipedes with an appropriately labeled contact pesticide may be required for several nights. Removal with a shop-vac works well and may be the only acceptable solution. Indoors, they are most easily removed with a vacuum.