Issue No. 145
H. V. Weems, Jr., and H. F. Loomis
June, 1974
Introduction
Two polydesmid species of millipeds most frequently encountered in Florida greenhouses, nurseries, and homes are the hothouse or greenhouse milliped, Oxidus gracilis (Koch) (fig. 1a), and the tropical milliped, Orthomorpha coarctata (Saussure) (fig. 1b). both often occur in large numbers, causing concern that they may be causing serious injury to plants. McDaniel (1931) reported that Oxidus gracilis was a serious problem in forcing-houses because it ate tender shoots and roots of plants. However, extensive laboratory experiments with this species by Causey (1943) showed no evidence that either larvae or adults eat living plant tissue. Both immatures and adults feed on loam, manure, or leafmold. In nature these and other millipeds have a share in the beneficial work of reducing dead plant material to humus. Prussic acid and other corrosive secretions of these millipeds may aid in the precipitation of colloidal substances in the humus. Both Oxidus gracilis and Orthomorpha coarctata have been accused of eating living plants or their roots or tubers, but probably they were eating the necrotic tissue resulting from injuries caused by man or machines, insect or other animal bites or tissue killed by disease. While they may become somewhat pestiferous in houses or around or in swimming pools, they do little direct damage, and their soil conversion activities greatly outweigh any damage they may do. Another common concern of the homeowner is that these and other kinds 0f millipeds may be poisonous to humans. This mistaken belief probably is due to the superficial resemblance to the poisonous, many-legged centipedes, but millipeds are harmless to humans. While they do secrete free hydrocyanic acid from repugnatorial glands, they lack true poison glands. As a generalization they may be distinguished from centipedes by having 2 pairs of legs per body segment, whereas centipedes have 1 pair of legs per body segment. The mouthparts of millipeds are not adapted for biting or chewing, but are equipped with minute scrapers and combs for collecting soft, decaying materials. The only living plants that are eaten regularly by millipeds are the fleshy fungi.