Rolly pollies are familiar sights in gardens. These small, armored creatures spark curiosity about their origins and life stages. Many wonder if they transform into something different. This article clarifies their biological identity and unique life cycle, addressing the misconception of metamorphosis.
Understanding Rolly Pollies: What They Are
Despite common names like “roly-poly” or “pill bug,” these creatures are not insects. They are terrestrial crustaceans, belonging to the order Isopoda, making them more closely related to crabs, lobsters, and shrimp than to beetles or butterflies. Rolly pollies are unique as they are the only crustaceans that have fully adapted to living entirely on land. They typically measure between one-quarter and five-eighths of an inch long, with an oval body shape. Their bodies are distinctly segmented, covered by seven overlapping plates that give them an armored appearance.
A notable characteristic of rolly pollies is their ability to curl into a tight ball when disturbed or threatened, a defensive behavior known as conglobation. This action protects their softer undersides and helps them retain moisture, which is essential for their gill-like respiratory structures. They have seven pairs of legs, totaling fourteen, which differentiate them from insects that have only three pairs. This unique combination of features allows them to thrive in moist, dark environments, such as under decaying vegetation or garden debris.
Their Life Cycle: Do They Transform?
Rolly pollies do not undergo metamorphosis, the dramatic transformation seen in insects like butterflies. Instead, they grow through a series of molts, shedding their rigid exoskeleton to accommodate their increasing size. This molting process is distinctive for rolly pollies; they shed their exoskeleton in two halves. The posterior (back) half is shed first, followed by the anterior (front) half a few days later, a strategy thought to reduce their vulnerability to predators during this soft, unprotected period.
Reproduction involves the female carrying fertilized eggs in a specialized brood pouch called a marsupium, located on her underside. This pouch provides a moist, protected environment for the developing eggs, which can number from 1 to 200. Eggs hatch within this pouch after several weeks. The young emerge as miniature versions of the adults, sometimes called mancae, which initially have six pairs of legs and gain their seventh pair after their first molt.
These young rolly pollies remain in the marsupium for a few days to several weeks after hatching, feeding from the mother’s marsupial fluid before venturing out independently. They continue to grow larger by molting periodically throughout their lives, eventually reaching maturity. Rolly pollies remain rolly pollies throughout their entire life cycle, simply growing larger with each molt rather than changing into a different creature.