Roly polies, often called pill bugs, are common terrestrial crustaceans frequently encountered in gardens and damp environments. Despite their insect-like appearance, they are more closely related to aquatic crustaceans like shrimp and lobsters. These creatures are characterized by their segmented, oval bodies and their ability to roll into a tight ball when disturbed, a defense mechanism known as conglobation. Roly polies thrive in moist, dark places such as under rocks, logs, and leaf litter, where they decompose decaying organic matter and return nutrients to the soil.
Understanding Roly Poly Reproduction
Roly polies reproduce through internal fertilization, typically during warmer months. Following mating, the female deposits her fertilized eggs into a specialized brood pouch on her underside. This pouch, called a marsupium, is a unique feature among terrestrial crustaceans.
The marsupium protects developing eggs and young, providing a moist and secure environment. It is formed by overlapping plates, known as oostegites, which create a fluid-filled reservoir where the eggs can mature. The number of eggs carried within the marsupium can range from a few dozen to as many as 200, or even 250 in some species.
Identifying Pregnancy Signs
Observing a roly poly’s marsupium is the primary way to determine if she is pregnant. This brood pouch is located on the underside of the female’s body. When a female is pregnant, the marsupium will appear noticeably swollen and distended, often looking like a translucent or yellowish sac.
As the eggs or developing young (mancae) mature inside, they may become visible through the marsupium. They often appear as small, light-colored spheres or tiny, pale, miniature versions of the adult roly polies. To get a clearer view, one might gently pick up the roly poly and use a magnifying glass, allowing for a closer inspection of the underside. While a pregnant roly poly might seem larger or more rotund overall, the presence of the visibly full marsupium is the definitive indicator of pregnancy.
Life After Pregnancy
Once eggs develop sufficiently within the marsupium, they hatch inside the pouch. The newly hatched young are called mancae. These mancae are miniature versions of adult roly polies, pale or white in color, and initially possess six pairs of legs, acquiring their seventh pair after their first molt. They may remain within the mother’s marsupium for several days or weeks after hatching, continuing to grow and be nourished by marsupial fluid.
After this period, the mancae are released from the marsupium. Upon release, these tiny roly polies are independent and immediately seek out moist environments and small food particles. Their survival depends on maintaining moisture, as their gill-like respiratory structures require a damp habitat. They will undergo several molts as they grow, gradually developing into adult roly polies.