The greenhouse millipede, Oxidus gracilis, is a common nuisance pest, particularly in moist environments like greenhouses, basements, and gardens. Although not harmful, their presence in large numbers can be unsettling and indicates an underlying environmental issue. Understanding the millipede’s biology and preferred habitat is the first step toward effective control. This guide provides practical steps for preventing infestations.
Identifying the Pest and Its Attractants
The greenhouse millipede typically measures between three-quarters of an inch and one inch (18 to 25 mm) in length. Its body is dark brown to black, featuring a somewhat flattened top and pale cream-colored legs and lateral extensions known as paranota. Unlike insects, millipedes belong to the class Diplopoda, characterized by having two pairs of legs on most body segments.
They primarily feed on decaying organic matter, such as leaf litter, rotting wood, and compost. Their presence is a direct indicator of excessive moisture and abundant food sources. Millipedes lack the waxy outer layer found on insects, making them highly susceptible to desiccation. They seek out damp, cool, and dark conditions to survive. When their outdoor habitat becomes too dry, they are driven to migrate indoors in search of moisture.
Cultural and Physical Removal Strategies
Modifying the environment to make it inhospitable is the safest and most effective starting point. Addressing moisture is primary. This involves improving ventilation in enclosed areas like basements and crawl spaces to reduce humidity. Ensure that all watering of lawns or plants is done in the morning to allow surfaces to dry before nightfall.
Outdoor debris provides both shelter and food, so removal is necessary. Rake back heavy accumulations of mulch, leaf litter, and grass clippings from the structure’s perimeter. Firewood and lumber should be stored off the ground and away from the foundation walls to eliminate potential harborage sites.
For millipedes already inside, physical removal is the most appropriate control method. Use a vacuum cleaner to collect live and dead millipedes from floors and baseboards, then dispose of the vacuum bag outside in a sealed container. Aggregation traps can also be set up using pieces of damp cardboard or melon rinds placed in high-traffic areas for easy collection and disposal.
Targeted Chemical and Barrier Treatments
When cultural methods are insufficient, chemical and barrier treatments can be used. Focus on creating a chemical barrier around the structure’s entry points rather than broad-spectrum spraying. Residual pyrethroid insecticides, such as those containing bifenthrin or cyfluthrin, are recommended for outdoor perimeter treatments.
Apply liquid insecticides in a band around the foundation wall and adjacent soil. In areas with heavy mulch, rake the mulch back before application to allow the insecticide to penetrate the soil. Granular formulations, watered in after application, are another effective method for treating mulched areas and heavily thatched turf.
Desiccant dusts, such as Diatomaceous Earth (DE), provide a non-toxic physical barrier for entry points. This material works by damaging the millipedes’ exoskeleton, causing fatal dehydration. Apply the dust lightly into cracks, crevices, wall voids, and behind electrical outlets where millipedes may be entering.
When using any chemical treatment, particularly near food crops or around children and pets, always read and follow the product label directions. Ensure all treated areas are completely dry before allowing access. Avoid applying liquid insecticides where runoff could contaminate water sources, as these chemicals can be highly toxic to aquatic life.
Long-Term Prevention and Habitat Modification
Long-term habitat modification is necessary to eliminate the environmental conditions that allow millipedes to thrive. Structural exclusion requires sealing all potential entry points into the building. Use a quality caulk to fill cracks and gaps in the foundation, masonry, and around utility penetrations like pipes and wires.
Establish a dry, vegetation-free zone immediately surrounding the structure. Maintaining a band of bare ground or gravel next to the foundation creates a buffer that millipedes are less likely to cross. Routinely check for and repair any moisture sources, such as leaky outdoor faucets, damaged gutters, or poor surface drainage.