**Pillbugs** (*Armadillidium vulgare*), often called **Roly-Polies**, are terrestrial crustaceans (not insects) easily recognized by their ability to roll into a tight, defensive ball when disturbed. They are globally common and are primarily **beneficial decomposers** that aid in nutrient cycling by breaking down decaying organic matter. However, they are occasionally considered minor garden pests, particularly during periods of drought, when they may feed on tender seedlings, ripe fruits, or soft root vegetables near the soil surface.
Taxonomy and Classification
Pillbugs belong to the subphylum Crustacea, class Malacostraca, and order Isopoda. They are the only crustaceans that have fully adapted to life on land, though they still require high humidity and moisture. They undergo simple development. They are closely related to Sowbugs (*Porcellio* spp.), which are flattened and cannot completely roll into a ball.
Physical Description
Adult Pillbugs are oval, segmented, and typically measure $1/4$ to $1/2$ inch long.
- **Appearance:** Gray, dark brown, or black, with a hard, convex, protective shell (dorsal cuticle). They have seven pairs of legs.
- **Defense:** The ability to contract into a perfect sphere (**conglobation**) is their main defense mechanism against predators and desiccation.
- **Respiration:** They breathe through modified gill-like structures, which is why they must live in high-humidity environments.
- **Reproduction:** Females carry their eggs and young in a specialized pouch on their underside called a **marsupium**.
Distribution and Habitat
Pillbugs are cosmopolitan, having been transported globally through human commerce. Their habitat is restricted to dark, damp environments rich in organic material. This includes under logs, rocks, bricks, pots, mulch, heavy leaf litter, and compost piles. They are common in damp basements, crawl spaces, and along building foundations, especially where excessive moisture is present.
Behavior and Conflict
Pillbugs are nocturnal, spending the day hidden in damp areas and emerging at night to feed.
- **Beneficial Role:** Their primary ecological role is decomposition, converting decaying plant matter back into soil nutrients.
- **Minor Pest Damage:** Damage to living plants usually occurs only when populations are extremely high and preferred decaying matter is scarce (e.g., during drought). They may chew holes in the leaves of tender seedlings, or gouge ripe fruits (strawberries, melons) or tubers (potatoes) resting on the ground.
- **Nuisance Pest:** They are considered nuisance pests when they wander indoors, which is usually accidental. They cannot survive for long in the dry indoor environment.
Management and Prevention
Control focuses on reducing moisture and removing harborage sites; chemical treatment is rarely necessary or effective.
- **Moisture Reduction (Crucial):** Improve drainage in gardens and around the home foundation. Eliminate leaky faucets and downspouts that keep soil constantly wet.
- **Harborage Removal:** Remove piles of wood, bricks, old boards, and excess debris near the house foundation. Reduce mulch layers to less than 2 inches, keeping it away from plant crowns.
- **Exclusion:** Seal cracks and crevices in the foundation and around ground-level doors and windows to prevent accidental entry into basements or crawl spaces.
- **Targeted Control:** If feeding on tender seedlings is a problem, use physical barriers (e.g., cut-off plastic bottles) or diatomaceous earth dusted around vulnerable plants.
Conservation and Research
Pillbugs are managed as benign, beneficial decomposers. Research focuses on their specialized adaptations for water retention, their role in heavy metal accumulation in soil, and their use as indicators of soil health and contamination.