WSU Extension

Hortsense

Common Insects & Mites : Sowbugs, pillbugs, and millipedes
(revision date: 4/30/2013)


Biology
Sowbugs (Porcellio spp.) and pillbugs (Armadillidium spp.) are not insects. They are crustaceans and thus are more closely related to crabs and shrimp. Sowbugs are grey and prefer very damp areas. Pillbugs are bluish-black; unlike sowbugs, they can roll up into a ball when disturbed. They tend to tolerate drier conditions than sowbugs. Both range from 1/4 to 3/8 inch in length when full-grown. These creatures are often considered pests by gardeners, however both usually feed on decaying or very soft plant matter and rarely damage healthy plant tissues. In many cases they are found in rotting damp wood, such as stumps or in cedar shakes with heavy moisture. Since they recycle valuable nutrients and facilitate the health of soil and plantlife, they should be considered beneficial creatures. Millipedes also live in and feed on moist, decaying plant material, and live in soils which contain such materials. Millipedes are members of a completely different phylum (Diplopoda). They are slow-moving, hard-bodied organisms with many segments, each segment bearing two pairs of legs. They may cause serious damage by eating small roots and tunneling into larger roots, bulbs, and tubers. They are frequently found in feeding wounds made in strawberries by slugs; in these cases, the fermentation juices seem to attract the millipedes.
Management Options

Non-Chemical Management
  • Remove damp, rotting wood where sowbugs and/or pillbugs reside.
  • To deter millipedes, avoid accumulating lots of organic matter in the soil. Avoid overwatering.
Select non-chemical management options as your first choice!

Chemical Management

None recommended.

Images
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Caption: Sowbug
Photo by: A.L. Antonelli
Caption: Pillbug
Photo by: A.L. Antonelli
Caption: Forest millipede
Photo by: R.D. Akre
Caption: Millipede
Photo by: L.J. du Toit