NPIPM:Oniscidea
Authors: Ashley Mueller, Buyung Hadi
Identification
Woodlice are not insects; they are a crustacean closer in relationship to shrimps and lobsters. Most woodlice are 1/4 to 1/2 inch in length, flattened in appearance, silver-gray in color, and they have seven pairs of legs.
Two common types of woodlice in the U.S. are the sow bug and pill bug. Sow bugs have tail-like appendages that project from their posterior. Pill bugs do not have these appendages; however, they are most recognized by their ability to roll into a tight ball when disturbed. As a result, they are often called “roly-polies”.
Habitat
Woodlice require high humidity, and they are often found under objects like flower pots and stones, during the day. At night, they often leave their natural habitats, and they may be found on sidewalks and patios. They can invade buildings from entry points like doors and voids in concrete block walls. If high numbers of woodlice are observed indoors, they are most likely breeding outside near the foundation. They cannot survive indoors for more than a couple of days unless the conditions are very humid. Sow bugs and pill bugs are scavengers, and they mainly feed on decomposing plants. Occasionally they feed on tender seedlings in a garden.
Life Cycle and Seasonal History
Female woodlice keep their eggs in a water-filled sac, called a marsupium, underneath their bodies for several weeks. After they hatch, the young woodlice stay inside the pouch for a few weeks. Once they leave the pouch and disperse, they undergo a series of 10 molts in about two years to become an adult. Adult woodlice live approximately two years, and they molt irregularly throughout their lifetime.
Human Interaction and Urban Impact
Woodlice are not medically or economically important. They can invade humid spots in a building and become nuisance pests. However, they do not cause injury to humans and pets, and they do not cause damage indoors.
Prevention and Management Approaches
Exclude woodlice from the building by sealing cracks and gaps in the foundation, doors, and windows. Remove grass clippings, leaves, and excessive amounts of mulch beside the foundation to prevent attraction for sow bugs and pill bugs. Water should not accumulate near the foundation, and downspouts and gutters should be functioning properly. Before bringing firewood into the home, check for the presence of woodlice. If the garden is susceptible to woodlice, consider raising produce like cucumbers, which rest on the soil, off the ground.
In the case of infestation, controlling humidity in harborage areas should limit the habitat for woodlice and reduce the infestation. Remove woodlice in the home by capturing and releasing them or by vacuuming them.
Other Online Resources
For information regarding labels of chemical control options, please visit NPIC MAPL
