If large populations of millipedes are present indoors, remove mulch, thick grass, piles of rocks or other items that shelter the insects outdoors. Keep grass short, or dethatch the lawn to promote drier conditions that aren't suitable for the millipedes, and seal the home to keep the insects out. After removing the insect's shelters and sealing the home, apply powdered pesticide to the affected areas indoors, and apply liquid spray-type pesticide outdoors to eliminate the insects.
Water lawns and gardens early in the morning to ensure the water evaporates quickly if millipedes are present. To seal the home, use tight-fitting window screens and doors, and seal cracks and crevices with caulking or another suitable material.
When applying pesticide to mulch or leaf litter, rake the area to remove the mulch or leaves before applying the pesticide, or apply enough liquid to ensure the pesticide penetrates the material to reach the soil. Indoors, apply boric acid or another suitable powdered pesticide to suspected entrance points.
Avoid applying powdered pesticides to damp areas, as this decreases the effectiveness of the insecticide. Remove live millipedes inside the home with a vacuum or broom. Millipedes produce a foul-smelling fluid that can cause allergic reactions. Avoid touching the insects whenever possible, and wash hands thoroughly if touching a millipede is unavoidable.