On cold and dreary April days when weather puts a crimp on activities of flamboyant insects such as bees and flies, one dependable place to find some action is under the leaf litter where decomposers busily recycle dead organic matter and are hunted by scary predators. Among the most common arthropods down under are millipedes. Millipedes belong to the subphylum called Myriapoda or “many footed” arthropods. Millipedes do not really have a million legs or a thousand legs for that matter despite being called “thousand leggers”. Most millipedes have fewer than 400 legs with each body segment usually bearing two pairs of legs. This is one good way to distinguish millipedes from their kin, the centipedes. Centipedes have but one pair of legs per body segment.
Millipedes are important recyclers of plant material. They eat dead things and occasionally plant roots and leaves of small seedlings. Female millipedes lay between 20 and 300 eggs in the spring that hatch into tiny grazers with only a few body segments bearing single pairs of legs. As the millipede molts and grows, body segments with two pairs of legs are added. Millipedes live two to seven years and can produce hundreds of offspring during their lifetime. This is why populations seem to explode in flower beds richly dressed with mulch. Millipedes do not bite or sting, but several species secrete noxious chemicals from glands lining their body. These chemicals include hydrogen cyanide and benzaldehyde, potent toxins and irritants that could make a lizard or toad think twice about messing around with these denizens of the mulch. Since secretions may be irritating and stain clothing or skin, it is a good idea to wash your hands after handling millipedes. As millipedes consume dead plants in leaf litter and mulch, they are hunted and consumed by their own fierce predators such as fast-moving centipedes.
Importance of a millipede body
Centipedes, so called “hundred leggers”, are also misnamed because most do not have a hundred legs. Our common garden centipedes when fully grown have roughly 30 legs. Unlike their cousins the millipedes, centipedes evolved the carnivorous life style. They are important beneficial predators of insects and other invertebrates in landscape beds. To capture and subdue prey, centipedes have evolved an awesome set of appendages beneath their head know as poison claws. These powerful claws grasp a victim and inject poison to kill it. Some species secrete sticky fluids to ensnare and immobilize hapless prey. Large tropical centipedes carry quite a wallop and capture snakes, lizards, and small mammals. Although I was fortunate not to be bitten while capturing centipedes, it is generally not a good idea to hold centipedes with bare hands. Their bite is painful and similar in intensity to a bee sting.
Keeping them out of your home
If you worry about millipedes or centipedes invading your home, two things can be done to reduce the chances of unwanted visitations. First, never apply mulch to landscape beds in a way that allows mulch to directly contact your foundation. Always leave a barrier of bare ground of at least a foot between the mulched bed and the house. This will limit the ability of myriapods and other unwanted guests to enter your home. Also, make sure that door sweeps are in good repair to reduce the chance that millipedes or centipedes will enter beneath basement doors.
Thomas Eisner’s books “The Love of Insects” and “Secret Weapons” and the web sites listed below were used as resources for this story and Professor Shultz helped with the identification of the arthropods. More information on the biology of myriapods can be found at the following web sites.