Roly Poly Body Structure
Roly polies, also known as woodlice, exhibit a segmented body structure that provides clues for distinguishing between sexes. Their bodies are divided into a head, a pereon (thorax), and a pleon (abdomen). The pereon consists of seven segments, each bearing a pair of legs, while the pleon is made up of six segments. Understanding the ventral, or underside, of the pleon is particularly useful for sex determination as it houses the relevant reproductive structures.
The pleopods are flattened, leaf-like appendages located on the underside of the pleon, primarily functioning in respiration. There are typically five pairs of pleopods, though the first two pairs are generally the most modified and important for sex identification. At the very rear of the body, two tail-like appendages called uropods extend outwards.
Identifying Male and Female Characteristics
Distinguishing between male and female roly polies primarily involves observing specific features on their ventral side, particularly the pleopods and the presence of a brood pouch. Female roly polies possess a specialized structure called a marsupium, which is a pouch formed by overlapping plates on their underside. This marsupium is where females carry and protect their eggs and developing young. When a female is gravid, the marsupium will appear visibly swollen and often yellowish or whitish.
Male roly polies, in contrast, do not have a marsupium. Instead, their first two pairs of pleopods are distinctly modified. These pleopods are typically elongated, more pointed, and often appear somewhat caliper-like or stylus-shaped. These modified structures are involved in sperm transfer during reproduction.
The pleopods of female roly polies are generally shorter and less conspicuous than those of males. While they still serve their respiratory function, they do not exhibit the same elongated or pointed shape. General body size or coloration are not dependable traits for determining sex in roly polies, as these can vary significantly based on age, diet, and environmental factors rather than sex.
Practical Tips for Examination
Examining a roly poly to determine its sex requires careful handling and good observation conditions. Gently scoop the creature onto a clean, flat surface, such as a piece of paper or a clear plastic lid, using a soft brush or a small spoon. This method prevents harm to the delicate animal during transfer. Avoid direct contact with your fingers, as this can injure their segmented bodies.
Once the roly poly is on the surface, allow it a moment to uncurl. You will need to carefully observe its underside. Using a magnifying glass or a jeweler’s loupe can significantly aid in viewing the small structures, especially the pleopods and the potential marsupium. Ensure adequate lighting, perhaps from a desk lamp, to illuminate the ventral surface clearly.
After your observation, gently return the roly poly to its original habitat. It is important to minimize the time the creature is out of its natural environment to reduce stress. This careful approach ensures the well-being of the roly poly while allowing for successful identification.