The small, segmented creature that curls into a tight ball when disturbed is a common inhabitant of gardens and damp environments worldwide. Known by many names, understanding what this animal is called, both scientifically and colloquially, reveals much about its characteristics and widespread presence.
Their Scientific Identity
These creatures are not insects. They are terrestrial crustaceans, more closely related to crabs, lobsters, and shrimp. The most common species is Armadillidium vulgare, often called the common pill bug. This species belongs to the order Isopoda and the family Armadillidiidae.
As isopods, they possess a segmented body typically measuring between one-quarter and one-half inch in length. They feature seven distinct pairs of legs, distinguishing them from insects. Their hard, armor-like outer shell provides protection and is composed of overlapping plates.
A World of Common Names
The “roly poly” goes by many common names across different regions. “Pill bug” is a widely recognized alternative, directly referencing its ability to roll into a compact ball. Another frequent term is “woodlouse,” particularly in the United Kingdom, where they are also known by names such as “chiggypig,” “penny sow,” or “cheesybug.”
In North America, terms like “potato bug” and “doodlebug” are also used. These numerous names arise from regional variations and descriptive characteristics, as there is no single universally adopted common name. The ability to curl into a ball, their appearance, or their preferred habitats often inspire these diverse monikers.
Distinctive Traits and Behaviors
One of the most recognized behaviors of these crustaceans is their ability to roll into a tight ball when disturbed, a defense mechanism known as conglobation. This action protects their softer underside from potential predators and helps them conserve moisture. Their segmented exoskeleton with flexible membranes allows for this rapid curling, effectively mimicking a small pebble.
These animals prefer damp, dark environments, often found under rocks, logs, leaf litter, and other decaying organic matter. This preference is due to their unique respiratory system; unlike insects, they breathe through gill-like structures that require a moist environment to function. If their gills dry out, they can suffocate.
Their diet primarily consists of decomposing organic material, making them detritivores. They consume decaying plants, wood, and other organic debris, playing a role in breaking down matter and returning nutrients to the soil. While generally harmless to humans and healthy plants, their presence indicates a moist environment, and they can occasionally damage young seedlings if present in very large numbers.