**Isopods** (order Isopoda) are a large group of crustaceans that includes terrestrial, marine, and freshwater species. The most common species encountered as nuisance pests are the terrestrial isopods, often called **pillbugs** (*Armadillidium vulgare*) or **sowbugs** (*Porcellio scaber*). They are often found in damp, dark areas under logs, rocks, and leaf litter. While they are crucial decomposers in the environment, they become structural pests when they invade basements and damp crawl spaces, or when their large populations damage garden seedlings and soft fruits.
Taxonomy and Classification
Isopods belong to the class Malacostraca, making them crustaceans—relatives of crabs, shrimp, and lobsters. They undergo simple development (egg, nymph, adult). Terrestrial isopods breathe using modified gills and must live in areas of very **high moisture** to prevent desiccation. They are sometimes mistakenly called insects, but their segmented bodies and seven pairs of legs identify them as crustaceans.
Physical Description
Isopods are small, oval, gray to brown, segmented creatures, typically 1/4 to 1/2 inch long.
- **Pillbugs (*Roly-Polies*):** Characterized by their ability to completely **roll into a ball** (conglobate) when disturbed, a defense mechanism.
- **Sowbugs:** Cannot roll completely into a ball and have two small, tail-like appendages (**urotergites**) protruding from the rear end.
- **Body:** Have a distinct flattened, segmented, oval body and **seven pairs of legs**.
- **Habitat:** Outdoors, they are found under mulch, stones, planters, and other materials that hold moisture; indoors, they are restricted to damp areas like basements, crawl spaces, and laundry rooms.
Distribution and Habitat
Terrestrial isopods are found worldwide. Their habitat is restricted to environments with consistently high humidity and moisture content. They cannot survive in dry conditions. They are most active at night when humidity is highest, or during cool, wet periods.
Behavior and Conflict
Isopods are beneficial decomposers, feeding mainly on decaying plant matter, fungi, and detritus.
- **Gardening Conflict:** While usually beneficial, large populations can become pests in gardens by chewing on **soft fruits** (like strawberries) that rest on the ground, or on **tender seedlings** and plant roots, causing minor damage.
- **Structural Nuisance:** Indoors, they are strictly **nuisance pests** and do not bite, sting, or carry diseases. Their presence indicates a severe moisture problem within the structure. They enter buildings through gaps and cracks near the foundation, but quickly die once they reach dry indoor air.
- **Ecological Role:** They are highly valuable in ecosystems for recycling nutrients back into the soil by breaking down dead leaves and wood.
Management and Prevention
Control is integrated pest management (IPM), focusing almost entirely on moisture reduction and exclusion.
- Eliminate the food and water source. Ventilate damp basements and crawl spaces using fans or dehumidifiers.
- Repair leaky faucets, pipes, and downspouts that keep soil near the foundation perpetually wet.
Conservation and Research
Isopods are managed as beneficial detritivores in ecology. Research focuses on their physiological mechanisms for survival in terrestrial environments despite being crustaceans, and their role in breaking down pollutants in soil systems.