Millipedes normally live outdoors but may become nuisance pests indoors by their presence. At certain times of the year (usually late summer and autumn) due to excessive rainfall or even drought, a few or hundreds or more leave the soil and crawl into houses, basements, first-floor rooms, up foundation walls, into living rooms, up side walls and drop from the ceilings. Some homeowners as early as late June have reported annoying populations accumulating in swimming pools. Fall migrations during rainy and cool weather may result as a natural urge to seek hibernation quarters. Heavy continuous rainfall in newly developed wooded areas with virgin soil (decaying organic matter habitats) are often troublesome sites. Millipedes do not bite humans nor damage structures, household possessions or foods. They can give off a disagreeable odour and if crushed, leave an unsightly mess.
Millipedes, or “thousand-legged worms”, are brownish-black or mottled with shades of orange, red or brown, and are cylindrical (wormlike) or slightly flattened, elongated animals, most of which have two pairs of legs per body segment, except for the first three segments which have only one pair of legs. Antennae are short, usually seven-segmented, and the head is rounded with no poison jaws. Their short legs ripple in waves as they glide over a surface. They often curl up into a tight “C” shape, like a watch spring, and remain motionless when touched. They range from 1.27 to 3.17-cm long depending on the species. They crawl slowly and protect themselves by means of glands that secrete an unpleasant odour.
LIFE CYCLE & HABITS
Millipedes can be long-lived, sometimes up to seven years. They overwinter as adults and lay eggs singly or in small groups in the soil. Some females lay between 20 to 300 eggs (fertilisation is internal), which hatch in a few weeks with young reaching adulthood in the autumn. Some reach sexual maturity the second year, while others spend four to five years in the larval stage.
Millipedes are attracted to dark, cool, moist environments, usually going unnoticed in the summer due to their nocturnal habits (activity at night) and tendency to disperse. They feed on living and decomposing vegetation and occasionally on dead snails, earthworms and insects. Slight feeding injury can occur on soft-stemmed plants, in gardens and greenhouses. They cannot tolerate water-saturated soil, which forces them to the surface and higher ground. Likewise, dry, drought conditions can stimulate migration. In the autumn, it is believed they may migrate for better overwintering sites. If one or all of these conditions exist, sometimes hundreds or thousands of millipedes are found in garages, first floor rooms and basements. Others believe that migration may occur when the food supply dwindles in October and November.
These creatures are usually abundant in compost piles and heavily mulched ornamental plantings, moving out shortly after sunset sometimes into dwellings. Over the past years, they have migrated in large numbers during a period of unusually warm weather for the time of the year (23 degrees C) and then would immediately stop when a quick drop in temperature (cold snap) occurred. Anyone handling these creatures without gloves will notice a lingering odour (hydrogen cyanide-like), and the fluid may be harmful if rubbed into the eyes. If crushed, millipedes may stain rugs and fabrics.
Millipedes, related to lobsters, yabbies and prawn, require moist habitats and areas of high humidity. It is important to keep the house and outside area as dry as possible.
Millipedes prefer moist, decaying organic matter (similar to forest soil) and shade. Always keep compost piles, grass clippings, rotting wood, leaf piles, plant debris, stones, etc. away from the house foundation as far as practical to reduce moist, damp, dark places where feeding and reproduction can occur. Be sure to check for wood embedded or buried in the soil.
Also, ivy beds and mulch near the house may become a favoured habitat. Rake and remove trash or leaf litter in a strip three feet wide surrounding the house foundation if practical, exposing the soil surface to drying from the air and sunlight. Repair and seal cracks and openings in the foundation wall and around door and window frames with caulking compound and weather stripping.
Properly ventilate basements and sub floor crawl spaces to eliminate excess moisture. Indoors, many will die of desiccation (drying out) and can be collected by broom and dustpan, vacuum cleaner or other mechanical means and discarded.
Total control of millipedes during migration periods is difficult. Try to locate the most infested area or cause of infestation (nearby bush, pastures, lake sides, river areas, etc.). Outdoors, spray a protective barrier thoroughly soaking the soil in a 1.5 to 4.5 metre band around the house. Also, thoroughly spray the sides of the house up to the level of the first story windows, especially across doorways and other openings. The carbamate insecticides such as propoxur (Baygon), bendiocarb (Ficam) or carbaryl (Sevin) give the fastest knockdown compared to the other groups of insecticides. Wettable powder formulations provide the best soil residual control. If foundation plantings are heavily mulched, insecticides may have to be rodded down to the soil beneath the mulch. Repeat applications at weekly intervals may be needed.
Treatment of peat moss, mulch, wood chips, leaves, etc. used in landscaping around the house is important. Subsequent water sprinkling will carry the insecticide down into the soil where these creatures hide. Do not expect immediate kill since control may be slow (three to six days or more). Baygon bait works well when scattered along the house foundation providing fast knock-down. Additional pesticides such as amorphous silica gel (Drione, Tri-Die), boric acid (Perma-Dust), chlorpyrifos (Duration, Dursban, Empire, Engage, Tenure), diatomaceous earth (Answer), diazinon, esfenvalerate (Conquer), pyrethrins (Exciter, Kicker, Microcare, Pyrethrum, Safer) and resmethrin (Vectrin) can be used. Only the licensed pest control operator or applicator can use bendiocarb + pyrethrins (Ficam Plus), cyfluthrin (Optem, Tempo), cypermethrin (Demon, Cynoff, Cyper-Active, Vikor), deltamethrin (Suspend), lambdacyhalothrin (Commodore), permethrin (Dragnet, Flee, Prelude, Torpedo) and tralomethrin (Saga). Fluvalinate (Mavrik, Yardex) is used outdoors. Indoors, if needed, certain formulations of Ficam and Baygon household spray formulations will give some residual, spot or crack and crevice control while space treatments of pyrethrins or resmethrin will paralyse or kill by contact. Always read the label and follow directions and safety precautions.
William F. Lyon
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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