Woodlice are terrestrial crustaceans belonging to the order Isopoda, making them closely related to crabs and shrimp. These small, segmented creatures have successfully adapted to life on land, yet they remain dependent on moist environments to breathe through gill-like structures. This unique biology dictates a specialized diet that places them at the foundation of numerous terrestrial ecosystems. Their feeding habits are finely tuned to ensure the cycling of necessary nutrients.
The Primary Role: Decomposers of Organic Matter
Woodlice are classified as detritivores, meaning their primary food source is decaying organic matter found in damp, dark places. They play a significant role as nature’s recyclers, consuming the bulk of the dead plant material that accumulates on the forest floor and in gardens. This diet typically centers on leaf litter that has already begun to soften and decompose. By breaking down tough materials like cellulose and lignin, they initiate the essential process of nutrient return to the soil.
The woodlouse digestive system is adapted to process this partially decomposed food. They are particularly attracted to the fungi and molds growing on the decaying matter, as these microorganisms predigest the plant material, making the complex organic compounds easier for the woodlice to absorb. They also consume rotting wood, but only after it has become thoroughly compromised and softened by moisture and fungal growth.
This constant consumption of detritus is a service to the environment, as the woodlice convert the dead material into smaller fragments and nutrient-rich fecal pellets. These pellets are then more easily processed by other soil organisms, further speeding up the entire decomposition cycle. Woodlice also occasionally consume fallen, dead insects, providing a minor source of supplementary protein.
Essential Dietary Needs Beyond Decay
Beyond bulk detritus, woodlice have specific nutritional requirements tied to their crustacean lineage and their need to grow. The most notable of these is a substantial need for calcium, which is the primary mineral component of their hard exoskeleton. Because they must periodically shed their outer shell in a process called ecdysis to allow for growth, they must find ways to replenish this lost calcium rapidly.
To conserve this mineral, woodlice store calcium carbonate in specialized sternal deposits before molting. They then reabsorb this stored calcium to harden the new shell after the molt is complete. Furthermore, they often engage in coprophagy, or the consumption of their own shed exoskeleton (exuviae), to recover up to 80% of the calcium that would otherwise be lost.
The moisture content of their food is another dietary consideration linked directly to their survival. Woodlice lose water easily through their gill-like respiratory structures and cannot drink free-standing water. They must therefore obtain most of their necessary hydration directly from the damp organic material they eat. Consequently, moist food sources, such as damp leaf litter and rotting fruit, are preferred because they satisfy both nutritional and hydration needs simultaneously.
What They Avoid and Why
Woodlice are generally not considered agricultural pests because they actively avoid consuming healthy, living plant tissue. Their digestive systems are optimized for the softer, pre-processed material of decay, and they lack the strong mouthparts and digestive enzymes needed to break down the defenses of healthy plants. If woodlice are observed feeding on live vegetation, it is typically an indication that their primary food sources have become severely depleted.
In such cases of scarcity, they may nibble on very tender plant parts, such as young seedlings, soft fruit like strawberries, or delicate roots. This is an opportunistic behavior rather than a preference.
Woodlice avoid environments that are too dry or exposed to direct sunlight, as these conditions rapidly lead to fatal dehydration. Furthermore, they avoid sound, dry wood, which is a common misconception about their diet. They only consume wood that is already rotten and water-logged, meaning they pose no threat to structural timber in homes. Their presence indoors is usually a sign of a high-moisture problem rather than an active infestation seeking to damage the home’s structure.