WSU Extension


Common Insects & Mites
Asian lady beetle 
Bark beetles 
Brown marmorated stink bug 
Brown soft scale 
California gallfly 
Conifer aphids 
Cottony camellia scale 
Cutworms and loopers 
Eriophyid mites 
Exotic longhorned beetles 
Fall webworm 
Lecanium scale 
Oystershell scale 
Pamphilid sawflies 
Pear slug 
Root weevils 
Sapsucker damage 
Shothole borer 
Sowbugs, pillbugs, and millipedes 
Spider mites 
Spotted wing Drosophila (SWD) 
Tent caterpillars 

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Caption: Sowbug
Photo by: A.L. Antonelli
Common Insects & Mites : Sowbugs, pillbugs, and millipedes
(revision date: 4/30/2013)

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.


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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