Tightly spiraled worms? You've got millipedes!
In recent days I have had many homeowners call, send photos and come in with samples of brown, tightly curled worms found in the garden, along pavers; under garage doors and welcome mats; and in the damp recesses of their basements. All are concerned at the vast numbers of these yucky bugs, and want to know what to do. They've all got millipedes.
Millipedes are not actually insects, but are arthropods related to insects. They don't harm food, clothes, furniture, or other items within homes, although just their presence can be disturbing. We're seeing a lot of them this year because excessive rainfall has forced them out of their normal environment in the soil to drier areas.
The most common millipedes are dark brown and reach 1 to 1 1/2 inches when fully grown. They are round and elongated, with many small legs. When dead or disturbed, they tend to curl into a tight coil. Millipedes do not bite or pose any danger to humans. They feed on rotting organic matter such as leaves and wood and rarely feed on tender green leaves and roots. They spend almost all their time in moist areas, such as under rocks or logs and in lawn thatch.
Tolerate millipedes when possible. If you must do something, try one or more of the following nonchemical methods. If these steps are not sufficient, then use insecticides as a last resort.
• Caulk or seal cracks and other openings in exterior foundation walls and around doors and ground-level windows by late summer.
• Remove leaf litter and decaying vegetation from around the foundation which provide food and shelter for millipedes. A border of bare soil next to the foundation also turns away millipedes.
• Trim and thin foundation planting so that ventilation permits the soil to dry more quickly near the foundation.
• Allow the soil near the house to dry between waterings. Roughening the soil surface will speed drying and will work plant materials into the soil where it is unavailable to millipedes.
• Reduce thatch in your lawn to discourage millipedes. This is best done by dethatching in early fall.
Outdoors: If millipede numbers are still higher than you can tolerate despite these nonchemical steps, supplement your efforts with an insecticide application. Apply a liquid insecticide around the building's foundation and the adjacent ground in a band to help keep pests out. Common insecticides available to the general public for treating building foundations include: bifenthrin, cyfluthrin, deltamethrin, and permethrin.
You may also choose to apply a granular insecticide to the perimeter, such as deltamethrin, lambda-cyhalothrin, or permethrin. Be sure to buy an insecticide labeled for outdoor use around buildings. Chemical treatment will be less effective if food and shelter exist near the foundation and there are available cracks and spaces for pests to enter the building. Apply an outdoor insecticide in late summer or early fall when millipedes are first noticed indoors.
Indoors: Millipedes often die soon after entering homes because it is too dry, making an insecticide application unnecessary.