Pill Bug or Sow Bug Identification: Telling It From Look-Alikes
Quick answer
Pill bugs / Sow bugs: 4 marks to check, what they are often confused with, whether they bite or sting, and where they turn up, quoted from university entomology and IPM sources.
Updated 2026-09-10 · Sources: UC IPM, Penn State Extension
Found one? Take a photo to identify it.
Download on the App StoreWhat are the key facts?
- Group: Class Crustacea, order Isopoda; not insects and not arachnids
- Body plan: Body oblong to oval with an arched or half-domed back; adults have seven pairs of thin legs and two antennae; the body has seven larger thoracic segments and six smaller abdominal segments.
- Size: Adults are about 1/3 to 3/4 inch long; juveniles are about 1/12 inch long.
- Bites or stings: The source explicitly states these terrestrial isopods are harmless to humans.
- Where you find them: Mostly hidden under organic litter or other debris on the ground, and beneath low-growing plant parts.
How to tell it is one of the pill bugs / sow bugs
- When disturbed, pillbugs curl into a ball, while sowbugs cannot roll into a complete ball and typically scurry away instead.
- Tail feature: pillbugs have a smooth, rounded rear end, while sowbugs have distinct appendages protruding from their rear.
- One common name for the pillbug is "roly-poly" (also "woodlouse").
- Neither an insect nor a true bug, but a crustacean in the order Isopoda.
Bites and stings
The source explicitly states these terrestrial isopods are harmless to humans. Seek medical care promptly for severe symptoms or any allergic reaction.
Pest or beneficial?
Overall important decomposers of organic matter (a beneficial role), but occasionally feed on seedlings, new roots, lower leaves, and fruit; in large numbers they can chew on fruit, succulent plant parts, seedlings, and vegetables that touch moist soil.
Where they turn up
Mostly hidden under organic litter or other debris on the ground, and beneath low-growing plant parts.
How to photograph it for identification
Get as close as your camera will focus, from directly above, in daylight or a bright lamp. Include the whole body with the legs and antennae in frame; a second shot from the side shows wings and body segments. Put a coin or ruler next to it for scale. For a bite or a bug found on skin or bedding, photograph the bug itself, not the mark. The app names the likely group; use the list above to confirm.
FAQ
Do pill bugs / sow bugs bite or sting?
The source explicitly states these terrestrial isopods are harmless to humans. Seek medical care promptly for severe symptoms or any sign of an allergic reaction.
What is the quickest way to recognize pill bugs / sow bugs?
When disturbed, pillbugs curl into a ball, while sowbugs cannot roll into a complete ball and typically scurry away instead.
Are pill bugs / sow bugs a pest?
Overall important decomposers of organic matter (a beneficial role), but occasionally feed on seedlings, new roots, lower leaves, and fruit; in large numbers they can chew on fruit, succulent plant parts, seedlings, and vegetables that touch moist soil.
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Sources
- UC IPMipm.ucanr.edu/home-and-landscape/pillbugs-and-sowbugs/
- Penn State Extensionextension.psu.edu/introduction-to-invasive-terrestrial-isopods
Compiled by the InsectLens editorial team
Every fact on this page is taken from the sources listed above; numbers and prices are copied from the source, and prices name the guide or auction and its date. Research and drafting were assisted by AI, and each claim was then checked against the cited sources. Checked 2026-09-10. We do not buy, sell or grade items; the app identifies what you photograph and points you to these references.