Sowbugs and Pillbugs

-- Woodlice, roly poly bugs, wood bugs --

Summary: Normally these small land crustaceans don't harm anything in the garden. Occasionally high numbers cause damage to tender seedlings but control is generally not needed. Sowbugs/pillbugs sometimes enter homes to escape saturated soil or in search of water when it is dry. They cause no damage in homes and can be swept up and tossed back into the landscape.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

Sowbugs, pillbugs, woodlice identification

Sowbugs, pillbugs, or woodlice [more pictures] are small land crustaceans, more closely related to shrimp than insects. They are roughly 1/4" long, gray to brown in color, have many pairs of legs and a segmented body, and are often found in groups under rocks or debris where the soil is damp. Pillbugs roll into a ball when disturbed, sowbugs do not roll up this way but otherwise the two are very similar. The term woodlice (singular woodlouse) is used to describe the group in general.

Sowbugs and pillbugs normally don't harm garden plants. They feed mostly on dead organic debris but occasionally may damage young garden seedlings. Two situations occur that do cause gardeners and homeowners some concern however.

sowbugs and pillbugs

Sowbugs and pillbugs are found in moist habitats under rocks and debris. Photo by E. DeAngelis.

Sometimes tender young garden seedlings are damaged, the damage is similar to slug damage. This plant damage only occurs when very high populations of these critters are allowed to develop and when very young plants are present. Plant injury is pretty rare and can usually be easily managed or outgrown if plants are otherwise healthy.

The second way sowbugs and pillbugs cause problems is when they enter homes following rains when outside soils become saturated, or in search of water when it is extremely dry. Sowbugs found indoors won't cause any damage and can be simply swept up.

other common names: woodlice (wood louse), lawn shrimp, rollie-pollie (pillbug), rolly-polly, tumblebug, doodlebug, roly poly bug

Control (if needed)

In one sense high numbers of these critters is really a good thing-- it means that your garden soils are rich in organic matter and healthy. You can reduce the populations, however, by reducing the amount of organic matter, such as compost, that you add to the garden and by cutting back on the frequency of watering. If the soil is allowed to go through natural dry/wet cycle sowbug and pillbug numbers will be reduced.

Gardeners can use diatomaceous earth (see Using Diatomaceous Earth for Pest Control) to manage sowbug and pillbug damage to young seedlings. Place a thin layer of this natural product directly over the seed bed. There is also a new formulation of Sluggo slug bait that contains spinosad, a natural insecticide that can be used to safely manage earwigs and sowbugs/pillbugs in the garden (see Using Slug Baits).

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