Pill bugs (roly-polies) are terrestrial crustaceans, related to shrimp and crabs, not insects. They use gill-like structures and require moist environments, typically decomposing dead organic matter like leaf litter and decaying wood. When populations explode or conditions become too wet, their diet shifts, and they begin feeding on tender live plants, transforming them into garden pests.
Are Pill Bugs the Real Culprit?
Pill bugs are small, oval, gray to brown creatures, generally measuring between one-quarter and one-half inch long. They are easily identified by their segmented, armored bodies and their defensive ability to roll completely into a tight ball when disturbed. This characteristic distinguishes them from the closely related sow bug, which is flatter and possesses two small tail-like appendages. Pill bugs primarily consume decaying plant material, which is beneficial for soil health and nutrient recycling.
When their preferred food source is scarce or populations are high, they will target vulnerable garden plants. Their feeding is typically concentrated at the soil line, leaving irregular holes in leaves, stems, and soft fruits like strawberries and melons. Pill bugs are nocturnal, so scouting for them with a flashlight at night is the most reliable way to confirm damage to new seedlings or soft plant tissue. Damage to the stem near the base often causes young plants to collapse entirely.
Eliminating Habitat and Physical Traps
The most sustainable method for controlling pill bug populations involves removing the dark, damp environments they need to survive. Since these crustaceans rely on moisture to breathe, reducing excessive wetness in the garden is highly effective. This involves improving soil drainage and being cautious not to overwater plants, especially those in containers or raised beds.
Removing organic debris like thick layers of mulch, leaf litter, and old wooden boards near vulnerable plants eliminates their primary hiding spots and daytime shelter. Materials that cannot be removed, such as stepping stones, should be elevated slightly off the ground to allow the soil underneath to dry out. This habitat modification forces the pill bugs to seek moisture elsewhere, often leading to dehydration.
Physical trapping provides a non-toxic way to remove large numbers of pill bugs quickly. A common method is the beer trap, where a shallow container is sunk into the soil so the rim is level with the surface and filled with beer or yeast water. The scent attracts the pill bugs, which crawl in and drown. Alternatively, placing hollowed-out halves of citrus rinds or dampened, rolled-up newspaper in affected areas overnight will lure them into moist shelter for manual disposal the next morning.
Active Killing Agents
When environmental controls are insufficient, targeted active agents can be used to kill pill bugs. Diatomaceous Earth (DE) is a popular organic control that acts as a physical insecticide. It is a fine powder made from the fossilized remains of diatoms, which are sharp, microscopic particles of silica.
The abrasive edges of the DE particles cut through the pill bug’s outer waxy layer, causing them to lose moisture rapidly and die from desiccation. For effectiveness, the food-grade DE must be applied as a thin, dry layer around the base of plants or where pill bugs congregate, as it becomes inert once wet. This method is a physical control, meaning the pest must crawl across the powder to be affected.
Iron phosphate baits, commonly sold for slug and snail control, are also effective against pill bugs. When ingested, the iron phosphate disrupts the crustacean’s digestive system, causing them to stop feeding and eventually die. These granular baits are considered less harmful to pets and wildlife than older metaldehyde products, as iron phosphate is a naturally occurring compound. For spot treatments, certain insecticidal soaps or pyrethrin-based sprays can provide contact kill, but they should be used sparingly and directed only at the pests.