Rolly pollies, also known as woodlice or pill bugs, are common inhabitants of gardens and damp environments around the world. These small, segmented crustaceans often curl into a tight ball when disturbed, a defense mechanism that gives them their popular name. Many people wonder how these creatures, which seem to thrive in moist conditions, obtain the water they need to survive. It turns out that their methods for taking in water are quite distinct from what most people might expect.
How Rolly Pollies Absorb Water
Unlike mammals, rolly pollies do not typically drink water in liquid form. Their primary means of acquiring moisture involves absorbing it directly from their surroundings and from the food they consume. They obtain a significant portion of their necessary hydration from the decaying organic matter that makes up their diet, such as rotting leaves, wood, and fungi. This decaying material naturally contains a high moisture content, which the rolly pollies extract as they digest it.
Beyond their diet, rolly pollies also absorb environmental humidity through their permeable exoskeleton, or cuticle. Their outer body covering is not fully waterproof, allowing for a continuous, passive uptake of water vapor from the air or moisture from damp surfaces. This absorption process is constant, enabling them to maintain their internal water balance as long as they are in a sufficiently humid environment. The efficiency of this passive absorption is important for their survival.
Their Unique Respiratory System
Rolly pollies possess specialized structures on their underside that facilitate both gas exchange and water absorption. These unique respiratory organs, often referred to as pseudotrachea or pleopodal lungs, are more akin to gills than the lungs found in terrestrial vertebrates. Located on the pleopods, which are flattened appendages on their abdomen, these structures are kept moist to allow for the efficient diffusion of oxygen from the air into their bloodstream.
These moist, gill-like surfaces are important for breathing and also play a role in their overall hydration. The large surface area and thin membranes of the pseudotrachea enable them to absorb moisture directly from the humid air around them. This dual function means their respiratory system is intrinsically linked to their water balance, making high environmental humidity a constant requirement for both breathing and staying hydrated. The reliance on these moist surfaces explains their preference for damp habitats.
Why Moisture is Crucial for Survival
The unique physiology of rolly pollies, particularly their gill-like respiratory system and permeable exoskeleton, makes them highly susceptible to desiccation. They lose water rapidly when exposed to dry air, which can quickly impair their breathing and threaten survival. This rapid water loss necessitates a constant search for and retention of moisture in their environment.
To counteract water loss, rolly pollies exhibit several behavioral adaptations. They are primarily nocturnal, emerging during cooler, more humid nighttime hours when evaporation rates are lower. During the day, they seek refuge in microhabitats that offer high humidity, such as under rocks, logs, leaf litter, or within decaying wood. They often congregate in these damp areas, further reducing individual water loss and creating a more favorable moist environment for the group.