Small, segmented creatures often seen scurrying across damp soil or curling into a sphere are commonly known as “rolly pollies.” Many people wonder if these backyard dwellers are the same as “pill bugs.” This question frequently arises due to their similar appearance and shared habitats, leading to a common point of confusion.
Unraveling the Names
“Rolly polly” is a common name for terrestrial crustaceans that roll into a tight ball when disturbed. This informal term primarily refers to pill bugs, members of the family Armadillidiidae. Scientifically, these creatures are classified within the order Isopoda, a diverse group of crustaceans. The ability to conglobate, or roll into a ball, is a defining characteristic of the Armadillidiidae family, distinguishing them from other isopods.
Key Characteristics of Pill Bugs
Pill bugs, also known as rolly pollies, are small terrestrial crustaceans, typically one-quarter to three-quarters of an inch long. Their oval bodies are covered by a segmented, armor-like exoskeleton, resembling a miniature armadillo. They possess seven pairs of legs. This segmented structure allows them to curl into a perfect sphere, a defense mechanism known as conglobation.
This rolling protects their softer undersides from predators and helps conserve moisture. Pill bugs thrive in moist, dark environments, such as under rocks, logs, leaf litter, and in compost piles. They are primarily decomposers, feeding on decaying organic matter like dead leaves and plants, playing a beneficial role in nutrient cycling in ecosystems. These creatures are generally harmless to humans and plants, though they may occasionally feed on tender seedlings or fruits that touch the ground.
Pill Bugs and Sow Bugs
Sow bugs are another group of terrestrial crustaceans often confused with pill bugs. While both belong to the order Isopoda and share a similar appearance, a key difference lies in their defensive behaviors. Unlike pill bugs, sow bugs cannot roll completely into a ball when threatened; instead, they scurry away or remain flattened.
Sow bugs have two prominent tail-like appendages, called uropods, protruding from their rear end. Pill bugs, in contrast, either lack these visible appendages or have them much less noticeable, allowing for their complete spherical conglobation. Both share similar damp, dark habitats and contribute to decomposition by feeding on decaying plant matter. The ability to roll into a ball and the presence or absence of these tail-like structures serve as reliable indicators for differentiating between these two common isopods.