Roly polies, also known as pill bugs or woodlice, are familiar invertebrates often found inhabiting damp, dark places in gardens and under rocks. These crustaceans are known for their segmented, oval bodies and their characteristic ability to roll into a tight ball when disturbed. While they are harmless decomposers, many people are curious about the intricacies of their biology, including how to distinguish between males and females. Understanding their subtle anatomical differences requires close observation and a bit of patience.
Identifying Relevant Body Parts
Determining the sex of a roly poly primarily involves examining the underside of its abdomen. Key structures to observe are the pleopods, small, flattened appendages located on the ventral side of the abdominal segments. While present in both sexes, their appearance differs significantly. Females may also have a marsupium. These features are quite small, requiring careful attention for accurate identification.
Distinguishing Males from Females
The most reliable method involves observing the structure of their pleopods. Male roly polies possess two distinct, modified pleopods that appear as pointed, rod-like structures. These are the first two pairs, located towards the front of their abdominal underside, adapted for sperm transfer. These modified appendages are rigid and extend slightly from the body.
Female roly polies, in contrast, lack these prominent, pointed pleopods. Their pleopods are flatter and less conspicuous, without the hardened, rod-like appearance seen in males. Instead, mature female roly polies, particularly during their breeding season, may develop a marsupium. This is a soft, fleshy pouch located on the underside of their thorax, where they carry their eggs and developing young. The marsupium can appear as a noticeable bulge or series of overlapping plates, depending on its stage of development and whether it contains eggs or young.
The marsupium is not always present on a female; it only develops when she is gravid or brooding. Therefore, its absence does not definitively indicate a roly poly is male. The presence of the pointed, rod-like pleopods remains the most consistent indicator for identifying a male. These differences are subtle and necessitate a magnified view for accurate identification.
Practical Tips for Close Observation
To effectively observe a roly poly and determine its sex, some tools and techniques can be helpful. A magnifying glass, or even a jeweler’s loupe, will significantly enhance visibility of the small anatomical features. Gentle handling is crucial to avoid harming the invertebrate; allowing it to crawl onto a soft paintbrush or carefully coaxing it onto your hand can prevent injury.
Placing the roly poly on a light-colored surface, such as a white paper towel, can provide a good contrast, making the underside structures easier to discern. Alternatively, a clear, shallow container allows for observation from multiple angles. Optimal lighting, perhaps from a desk lamp, will illuminate the delicate pleopods and any potential marsupium. After observation, it is important to return the roly poly carefully to its original habitat, ensuring its continued well-being.