Rolly Pollies, commonly known as Pill Bugs or Woodlice, are familiar inhabitants of gardens and damp environments across the globe. Despite their appearance, these creatures are not insects but are classified as terrestrial crustaceans, belonging to the order Isopoda, making them distant relatives of shrimp and crabs. A common misconception is that they hibernate through the colder months like mammals do. Their winter survival is actually a function of their environment and physiology, resulting in a significant metabolic slowdown rather than a deep, regulated sleep.
Dormancy Versus True Hibernation
Rolly Pollies do not engage in true hibernation, which is a state characterized by a regulated, deep drop in body temperature and metabolic rate. True hibernators maintain control over their body functions and can arouse themselves. The woodlouse’s survival strategy is a simple, temperature-dependent metabolic slowdown, best described as winter dormancy or inactivity.
This period of inactivity is not a regulated biological process like the torpor or diapause seen in some insects and mammals. Instead, their metabolism decreases because they are ectotherms, meaning their internal temperature and activity mirror that of their surroundings. When conditions become cold or otherwise unfavorable, their movement and energy expenditure are greatly reduced, which conserves the energy reserves they have built up during warmer months. They remain somewhat aware of their surroundings.
Finding Winter Shelter
The primary trigger for a Rolly Polly to seek refuge is the combination of cold temperatures and the need to retain body moisture. They are especially vulnerable to freezing, with temperatures below -2°C being lethal. They also lack a waxy cuticle, which means they are constantly at risk of desiccation. Their winter shelter must, therefore, provide both thermal insulation and a consistently humid microclimate.
They survive by retreating to sheltered locations that buffer them from harsh conditions. They will seek refuge underneath rocks, paving stones, or decaying logs. They also burrow into the upper layer of soil, deep leaf litter, or compost piles, sometimes going as deep as 0.25 meters into the ground. This layer of debris and soil acts as a natural insulator, often using the heat generated by decomposition to maintain a temperature above freezing and keeping the surrounding air moist.
What Rolly Pollies Do When Active
During the warmer, wetter seasons of spring, summer, and fall, Rolly Pollies are highly active detritivores, a function crucial to the ecosystem. Their diet primarily consists of decaying plant matter, such as fallen leaves, rotting wood, and other organic debris. By breaking down this material, they return nutrients to the soil, enhancing nutrient cycling. This activity is largely nocturnal, as they must avoid the sun and dry air to protect the delicate, gill-like structures they use for breathing.
Reproduction occurs when conditions are favorable, typically from late spring to early summer in northern climates. Females possess a specialized fluid-filled pouch on their underside called a marsupium, where they carry their eggs for approximately 8 to 12 weeks. After the young, known as mancas, hatch, they remain in the protective marsupium for a few days before emerging as miniature versions of the adults. A single female can produce between one and three broods annually, with each brood containing up to 300 eggs.