Description of greenhouse millipedes
Millipedes, also known as "thousand leggers," are common arthropods found in damp locations. The greenhouse millipede is often abundant in greenhouses (as the name implies) but is also found in potted houseplants and even may live outdoors in damp areas. The greenhouse millipede is different from the more common millipedes by being moderately flattened from top to bottom and lighter colored. They also have small "flanges" or ridges along the sides of each body segment.
Millipedes feed on damp and decaying vegetable matter and are not usually considered pests of houseplants. They can become a nuisance by migrating into buildings (especially basements) as accidental invaders, or by wandering about the house from potted plants or other damp areas. Although millipedes prefer to remain in moist locations they may wander into any part of the house. Millipedes do not feed upon building structures or furnishings and do not bite or sting. They are most active at night and usually hide during the day in moist locations.
Management of greenhouse millipedes
Control of greenhouse millipedes requires locating the source of the infestation. Check houseplants and damp areas in basements and crawl spaces. Millipedes discovered during the summer may originate outdoors under leaves and mulch, in window wells and similar locations.
If houseplants are infested you may decide to discard the plants. For plants you wish to save, remove any soil-covering mulch or moss and allow the potting soil to dry out as much as the plant can withstand between waterings. The soil surface, cracks along the edges of the pot and the area between the pot and saucer can be sprayed with a houseplant insecticide to further help eliminate millipedes. Millipedes in other areas can be treated with household insecticides such as "ant and roach killer" or "home pest control" products. Sweeping or vacuuming up and discarding wandering millipedes may be adequate control in some situations.
Millipedes wandering indoors during warm weather can be controlled by eliminating hiding spots next to the house (dead leaves, mulch, etc.) or by sealing cracks and crevices where they enter. Residual insecticides can be applied as sprays or granules in a 5- to 20-foot wide barrier around the building to reduce entry. The control treatments must be thoroughly applied in such a way as to get the insecticide down to the soil surface. For more information on outdoor use insecticides please see this article.
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