Roly-polies, commonly known as pill bugs or woodlice, are terrestrial crustaceans, not insects, related to crabs and lobsters. These adaptable invertebrates typically inhabit damp, dark environments, such as under rocks, logs, or leaf litter, where they aid in decomposition. Their ability to roll into a tight ball serves as a defense mechanism and helps conserve moisture.
Typical Roly Poly Size
Common roly-polies found in gardens are generally quite small. An adult common pill bug, scientifically known as Armadillidium vulgare, typically measures between 0.4 to 1.8 centimeters (0.15 to 0.7 inches) in length. Their body width usually ranges from 0.4 to 0.85 centimeters (0.16 to 0.33 inches).
What Makes a Roly Poly Grow?
Several factors influence a roly-poly’s growth and eventual size. Like all arthropods, they grow by shedding their rigid exoskeleton through molting. This process occurs in two distinct stages. Young roly-polies molt multiple times to reach adulthood, and adults continue to molt periodically. During these molting periods, they are particularly vulnerable to predators.
Environmental conditions significantly impact their development. Roly-polies possess gills, necessitating a moist environment to prevent desiccation. They seek refuge in humid, sheltered spots like under rocks, logs, and leaf litter to maintain moisture. Consistent humidity and moderate temperatures promote healthy growth.
Food availability and diet also play a substantial role in their size. Roly-polies are detritivores, meaning their diet primarily consists of decaying organic matter. They consume decomposing plant material such as dead leaves, wood, and fungi. A steady supply provides the necessary nutrients for their growth. They sometimes consume their own feces to reabsorb copper ions, which are essential for their physiology.
The lifespan of a roly-poly is another determinant of its final size. After hatching from eggs carried in a specialized brood pouch, young roly-polies remain there for approximately two months. They generally reach maturity around one year of age and can live for an average of 1.5 to 3 years. Some individuals, under optimal conditions, can live for up to four or five years, allowing for more growth cycles.
The Largest Roly Polies
While common garden roly-polies rarely exceed 1.8 centimeters, the question of how big a “roly poly” can truly get opens the door to their distant marine relatives. For truly impressive sizes, one must look to the ocean.
Giant isopods are deep-sea crustaceans from the genus Bathynomus, closely related to terrestrial roly-polies. These marine giants inhabit the cold, dark depths of the Atlantic, Pacific, and Indian Oceans, typically found between 170 and 2,140 meters (550 to 7,020 feet) below the surface. They feed on carcasses and organic debris that sink to the ocean floor.
Giant isopods vary by species but are dramatically larger than their land-dwelling cousins. “Giant” species measure 8 to 15 centimeters (3.1 to 5.9 inches), while “supergiant” species range from 17 to 50 centimeters (6.7 to 19.7 inches). Bathynomus giganteus commonly reaches 19 to 36 centimeters (7.5 to 14.2 inches). The largest confirmed specimen measured around 50 centimeters (20 inches).
This remarkable size is an example of “deep-sea gigantism,” where deep-sea organisms evolve to be much larger than their shallower-water relatives. These colossal marine isopods are distinct from backyard roly-polies.