Greenhouse Millipedes

Introduction

Native to Asia, the greenhouse millipede (Oxidus gracilis) is a cosmopolitan species commonly found throughout the eastern U.S. This species is also called the garden or hothouse millipede. Like other millipedes, greenhouse millipedes are generalist decomposers of organic matter and contribute to the recycling of nutrients in the environment. They are harmless and do not bite or sting.

Greenhouse millipedes can become a nuisance pest when their numbers become so excessive that they swarm over mulched flower beds and invade basements and other ground-level rooms in houses. At times, there can be thousands of millipedes moving across lawns and into houses.

Description

Greenhouse millipedes are slow-crawling arthropods with two sets of legs on each body segment. They range 16-21 mm (0.6-0.8”) long, and the body is slightly flattened. They are reddish brown to dark brown on their backs and paler on the sides and underneath. When touched, they may curl up and remain motionless (Fig. 2).

Life History

Millipedes lay eggs in the spring, and populations continue building during the summer. Populations can become very large when there is plenty of food and good habitat. Unfavorable conditions, such as excessive moisture, too little moisture, or a lack of food, may cause populations to disperse. Greenhouse millipedes occasionally cause problems around Virginia in the summer and fall. They are largely dormant over the winter, becoming active again as temperatures warm in the spring.

Habitat

Millipedes prefer damp, dark locations with abundant organic matter for food. Outdoors, they can be found under rocks, logs, and leaf litter. Around houses, areas that provide good millipede habitat include compost piles, excessive mulch beside foundations, wooded areas, and accumulated grass clippings or thatch. Greenhouse millipedes are often found under potted plants, door mats, trash cans, and other objects that are not moved frequently.

Damage

Greenhouse millipedes sometimes infest the garage, basement, or other ground-level areas of a house in the fall. Houses on wooded lots with walkout basements or patios under upper decks are often cool, shaded areas that can attract greenhouse millipedes. Their presence indoors is objectionable, but they often can’t survive indoors for long unless the humidity is sufficiently high. Greenhouse millipedes do not damage structural wood or wood furniture.

Greenhouse millipedes can be found in the moist habitat of hothouses, greenhouses, and other places where plants are propagated and grown. Greenhouse millipedes generally do not feed on plants unless the plants are already damaged or decaying. However, greenhouse millipedes may damage tender new plant growth when searching for moisture during droughty times when the soil and leaf litter are dry.

Control

Finding the source of the greenhouse millipedes may be useful, but this may not always help alleviate the problem. Populations of millipedes may build to large enough numbers that the habitat becomes overcrowded, and thousands of them migrate into yards and homes from other areas.

Rake and reduce mulch and excess grass clippings near the house. Correct any drainage or moisture problems outside of the house and in basements or other damp areas inside the house. In basements, consider using a dehumidifier and removing clutter where greenhouse millipedes can hide. Do not store firewood against foundations. Raise potted plants off the ground to be less attractive to greenhouse millipedes. Establish compost piles and flower beds away from the house.

Doors, including garage doors, should have functioning door sweeps. Remove any dead leaves or plant matter that accumulates in window wells. Basement windows should have good seals and tight-fitting screens. Seal any cracks, crevices, or holes in the foundation that may allow greenhouse millipedes and other arthropods access indoors. Sticky traps or double-sided sticky tape can be placed around entryways to catch greenhouse millipedes, but they will need to be replaced when covered with trapped arthropods to remain effective.

Vacuum or sweep up millipedes when seen inside the home. Insecticides labeled for indoor household pests are only partially effective, but will help in severe situations with excessive millipedes in the house. Widespread applications of insecticides outdoors during a mass millipede migration will do little to stop their numbers. Perimeter sprays around foundations work best if applied before millipedes begin migrating.

Revision

T. Dellinger, 2019 and 15 July 2025.