Sowbugs, often known as woodlice, are small, shelled creatures frequently encountered in damp, dark environments. Despite their common moniker, the sowbug is not an insect; it is a terrestrial crustacean, making it more closely related to shrimp and lobsters. These animals possess a grayish, segmented body and are a common sight when turning over a rock or decaying wood in a garden.
Defining the Sowbug
The sowbug belongs to the Order Isopoda, a suborder of Crustacea, a group mostly comprised of aquatic species. This classification explains its unique physical traits, especially its respiratory system, which depends on moisture. Sowbugs have gill-like structures, or pseudotracheae, on their abdominal appendages that must remain damp for gas exchange. This requirement for continuous moisture dictates their lifestyle and habitat selection.
Their body structure is characterized by a series of overlapping, armored plates protecting seven pairs of legs. An adult sowbug typically measures between one-third and three-quarters of an inch long and has a distinctly oval and flattened shape. Like other arthropods, they possess an exoskeleton that they must periodically shed, or molt, to grow. This molting process can leave them temporarily vulnerable to dehydration.
Sowbug Versus Pill Bug
A common point of confusion is the difference between a sowbug (Porcellio scaber) and its close relative, the pill bug (Armadillidium vulgare). The most reliable distinction is the pill bug’s defensive ability to roll completely into a tight, protective ball, a behavior known as conglobation. The sowbug cannot perform this action; when disturbed, it will only flatten out or attempt to run away, as its segmented plates do not allow for a full enclosure.
Visually, sowbugs can be identified by the presence of two distinct, small, tail-like appendages, called uropods, that protrude from the rear of their segmented body. Pill bugs entirely lack these rear appendages, presenting a smooth, rounded posterior when viewed from above. While both are generally slate-gray, the sowbug often has a flatter, more oblong appearance compared to the pill bug’s convex, dome-like body shape.
Habitat and Ecological Role
Sowbugs thrive exclusively in environments that provide high humidity and protection from direct sunlight, such as under logs, loose bark, rocks, and thick layers of mulch or leaf litter. Their nocturnal nature and preference for darkness help them avoid the desiccation that can be fatal to their gill-like respiratory system. Any place where moisture collects and organic material is present forms their ideal home.
Their primary function in the ecosystem is that of a detritivore, meaning they consume decaying organic matter, such as dead leaves, rotting wood, and other plant debris. By breaking down this material, sowbugs aid in the decomposition process, which releases trapped nutrients back into the soil. This recycling of organic material contributes directly to the fertility and overall health of the soil.
Assessing Damage and Control
Sowbugs are generally harmless to humans and do not bite, sting, or transmit disease. They are primarily nuisance pests when they venture indoors, seeking shelter in damp basements or crawl spaces. However, they cannot survive long in a dry indoor environment. Outdoors, they rarely damage healthy plants, as their diet consists of decaying matter.
Damage to tender plant tissues, such as delicate seedlings or soft fruits lying directly on the ground, usually only occurs when their preferred food source of decaying debris is scarce. Non-chemical control methods focus on minimizing the moisture and shelter they require. Effective steps include reducing excess organic material like woodpiles and heavy mulch near foundations and improving drainage. Sealing cracks and gaps in the foundation and around ground-level windows also prevents them from entering structures.