The woodlouse, often called a pill bug or roly-poly, is a common terrestrial crustacean belonging to the order Isopoda, making it more closely related to shrimp and crabs than to insects. They have successfully adapted to life on land, yet they retain a dependency on moist environments that often confuses homeowners about their habits. The frequent sighting of these small, segmented creatures under logs and in damp basements leads to the question of whether they actively consume the wood or merely use it for shelter. Understanding their unique biology clarifies this relationship.
The Definitive Answer: Woodlice Diet
Woodlice are classified as detritivores, meaning their diet consists entirely of decaying organic matter, positioning them as significant recyclers in the ecosystem. Their preferred food sources are primarily dead leaves, rotting vegetable matter, mold, and fungi that colonize decomposing materials. This diet is the reason they are frequently found in compost piles and under logs, where they help break down complex organic compounds. They lack the necessary biological machinery to effectively break down the tough cellulose and lignin found in sound, dry lumber. While they do possess cellulolytic enzymes that aid in digestion, these enzymes are mainly produced by endosymbiotic bacteria within their gut. Woodlice prefer to consume plant material that has already been softened and partially broken down by fungi and bacteria, making the nutrients more accessible. Therefore, any wood they consume is already significantly compromised and rotting, not structurally sound timber.
Attraction to Damp Environments
The woodlouse’s strong attraction to damp environments stems from its ancient aquatic heritage and unique method of respiration. Unlike insects, woodlice lack a waxy cuticle and breathe through gill-like structures called pleopods, located on the underside of their abdomen. These respiratory surfaces must remain consistently moist for effective gas exchange to occur. Without a waterproof exoskeleton, woodlice lose water rapidly through their cuticle via transpiration, making them highly susceptible to desiccation in dry air. A woodlouse actively seeks out microclimates with near-100% relative humidity to avoid drying out, which is why they aggregate under objects. Wood, especially when soft, water-damaged, or decaying, serves as excellent shelter because it retains moisture and provides the damp, dark conditions necessary for their survival. The presence of mold and fungi on this damp wood provides the necessary food source alongside the required humidity.
Impact on Structures and Management
For homeowners, the presence of woodlice in a structure is not a sign of a wood-boring pest problem, but rather an indicator of a pre-existing environmental issue. Woodlice do not damage sound, dry building materials, so they are not considered a pest to structural lumber. They are simply taking advantage of a high-moisture location that offers both shelter and a potential food source, such as fungal growth. Effective management strategies focus entirely on environmental control rather than chemical treatments. The most important action is to reduce the source of moisture and humidity that attracts them in the first place. This involves improving ventilation in crawl spaces and basements, fixing leaky pipes, and ensuring outdoor drainage directs water away from the foundation. Removing exterior sources of decaying matter, such as leaf litter, mulch, or wood piles that are in direct contact with the home’s perimeter, will eliminate their shelter and food supply.