In gardens and yards, a small creature often curls into a tight ball when disturbed. Known as a “rolly polly,” this organism is recognized by its distinctive defensive posture. These widespread invertebrates are frequently found in damp environments, prompting interest in their true nature and habits.
Understanding Their True Nature
Despite their common name and insect-like appearance, rolly pollies are not insects. They are terrestrial crustaceans, more closely related to crabs, lobsters, and shrimp. Scientifically, these creatures belong to the order Isopoda, a diverse group of crustaceans. The species known as “pill bugs” that exhibit rolling behavior are members of the family Armadillidiidae.
Their bodies are segmented, typically with seven pairs of legs, one pair for each thoracic segment. Unlike insects, they breathe through gill-like structures on their pleopods, specialized abdominal appendages. This respiratory system necessitates a moist environment for survival, as their gills must remain damp to function.
Where They Live and What They Eat
Rolly pollies, also known as woodlice, thrive in environments with consistent moisture and shelter. They typically inhabit damp, dark places like beneath rocks, logs, leaf litter, and garden debris. Their presence indicates organic decomposition in the soil, as they play an important role in breaking down organic materials in their ecosystems.
These detritivores primarily feed on decaying organic matter, contributing to nutrient cycling. Their diet consists mainly of dead plant material, including rotting leaves, wood, and fungi. They may also consume decaying animal remains or young plant sprouts if other food sources are scarce. By consuming this matter, they convert it into simpler compounds, enriching the soil and making nutrients available for plants.
The Art of Rolling Up
The most recognizable rolly polly behavior is its ability to curl into a tight, impenetrable sphere. This action, known as conglobation, serves as a primary defense against predators. When threatened by creatures like spiders, centipedes, or birds, rolling up protects their softer underside and appendages, presenting a hard, armored exterior.
Beyond predator defense, rolling up also helps these crustaceans conserve moisture. Their gill-like respiratory structures require a humid environment; prolonged exposure to dry conditions can be fatal. By coiling into a ball, they minimize surface area exposed to dry air, trapping moisture within their curled form. Only true “pill bugs” (Armadillidium vulgare) can roll into a complete ball, unlike other woodlice that only partially curl.