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Common Pillbug (Armadillidium vulgaris)


Detailing the physical features, habits, territorial reach and other identifying qualities of the Common Pillbug



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The Common Pillbug is a harmless and delightful way to introduce children to the world of insects, and though it goes by many different names, 'insect' isn't one of them.



Updated: 01/26/2021; Authored By Staff Writer; Content ©www.InsectIdentification.org
With a plated armor similar to armadillos, it is no mystery how the Genus name for this creature was determined. The Common Pillbug has a different common name in various regions of North America. In the West, they are called Sowbugs (though true Sowbugs are actually in a different genus and do not roll up like Pillbugs). In the Midwest, they are Roly-Polies. In the East, they are known as Wood Lice (not to be confused with the smaller insect known to infest human hair). Oddly enough, Common Pillbugs are not actually insects; they are isopods, making them close relatives to ocean creatures like crabs and other crustaceans.

Pillbugs do not bite and cannot sting. They are slow movers, making it easy to catch and observe them up close. Regardless of what you call them, they are fun to play with. When threatened or disturbed, they roll up into a tight ball, allowing their armor to protect their soft underbelly, head, and many legs. A gentle touch is enough to elicit this response. Pillbugs will remain in that defensive position until the threat is believed to have faded. They are patient. Their time in that defensive, balled-up posture often outlasts even the interest of children.

Pillbugs are considered primitive creatures, but they have an important role in the soil ecosystem. They are an abundant food source for insects and arachnids. Their own diet of rotting organic material like leaves and wood means they help cycle nutrients through the food web. They are easily found wandering under rocks, wood piles, fallen trees and other moist places where decomposition is likely taking place.




General Characteristics
Capability, Shape, Texture/Pattern, Benefits, Dangers
Harmless insect icon
Rounded insect body icon
Segmented insect icon




Taxonomic Hierarchy
Species Breakdown
Kingdom: Animalia
  Phylum: Subphylum Crustacea
    Class: Malacostraca
      Order: Isopoda
        Family: Armadillidiidae
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          Genus: Armadillidium
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            Species: vulgaris
Identifying Information
Size, Colors, Features
Scientific Name: Armadillidium vulgaris
Other Name(s): Sowbug, Wood Louse, Roly-Poly
Category: Isopod
Size (Adult; Length): 4mm to 18mm (0.15" to 0.70")
Colorwheel Graphic Colors: gray, black, yellow
Descriptors: shell, harmless, round, legs, ball, roll, plates, segments, armor

Common-Pillbug Video(s)




Pillbugs running as if their lives depended on it.
Relative Size Comparison
Typical Range Between 4mm and 18mm
Lo: 4mm
Md: 11mm
Hi: 18mm
Territorial Map*
U.S., Canada, and Mexico
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Territory map graphic of the country of Mexico
Contiguous United States shape map layer graphic
Alaska  
Hawaii  
Prince Edward Is.  
* MAP NOTES: The territorial heat map above showcases (in red) the states and territories of North America where the Common Pillbug may be found (but is not limited to). This sort of data is useful when attempting to see concentrations of particular species across the continent as well as revealing possible migratory patterns over a species' given lifespan. Some insects are naturally confined by environment, weather, mating habits, food resources and the like while others see widespread expansion across most, or all, of North America. States/Territories shown above are a general indicator of areas inhabited by the Common Pillbug. Insects generally go where they please, typically driven by diet, environmental changes, and / or mating habits.

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