The small, gray arthropods commonly known as rolly pollies, pill bugs, or woodlice are a frequent sight in gardens and under debris. These creatures are not insects but terrestrial crustaceans, making them closer relatives of shrimp and crabs. The answer to whether they kill plants is nuanced: they are primarily decomposers, but they can damage or kill vulnerable plants under specific environmental pressures. Understanding their biology is the first step in managing their presence in a home garden.
Rolly Pollies: The Garden’s Primary Decomposers
Pill bugs are classified as detritivores, meaning their diet consists almost entirely of dead or decaying organic matter. They function as nature’s recyclers, consuming rotting vegetation, dead leaves, mold, and fungi. This consumption is a beneficial process that speeds up the decomposition of organic material into the soil.
By breaking down this detritus, they return essential nutrients to the soil, improving its overall quality and structure for plant growth. Their activity helps in nutrient cycling, making those elements bioavailable for living plants.
Pill bugs breathe through gill-like structures that must remain moist, restricting them to damp, dark environments like under rocks, logs, and mulch. Their requirement for constant moisture is a defining characteristic of their habitat selection. They are most active at night when conditions are cooler and more humid, retreating to shelter during the day to prevent desiccation. This preference for damp, decaying material often indicates a healthy, organically rich soil ecosystem.
Conditions That Lead to Plant Damage
Damage to live plants is considered a secondary feeding behavior, triggered by environmental factors rather than being their primary food source. Pill bugs may switch to consuming live plant tissue when their natural food source of decaying matter becomes scarce or when populations become excessively large. This shift often happens when a garden is excessively clean of debris or when high population density creates competition for food.
Moisture stress is another significant trigger, as they may seek the water content within soft plant cells to supplement their hydration. This makes them pests during dry periods, even though they require humidity to survive.
The most vulnerable plants are tender seedlings, young shoots, roots, and soft fruits that rest directly on damp soil, such as strawberries, melons, and squash. Damage is typically concentrated near the soil line and may manifest as irregular holes in leaves or surface feeding on soft fruits. They are occasionally blamed for damage caused by other pests, as they readily feed on tissue already weakened or damaged.
Non-Chemical Strategies for Population Control
Reducing the availability of excessive moisture is an effective non-chemical approach to managing pill bug populations. Watering plants earlier in the day allows the soil surface to dry before the pill bugs become active at night. Improving drainage and avoiding overwatering makes the environment less hospitable.
Removing daytime hiding places significantly lowers their numbers near vulnerable plants. This involves reducing excess mulch, clearing up fallen leaves, and removing debris or boards that rest directly on the ground near seedlings. Ensuring good air circulation around plants also helps keep the soil surface drier.
Simple trapping methods can monitor or reduce localized populations without chemicals. Placing hollowed-out fruit halves, such as cantaloupe or citrus rinds, cut-side down acts as a bait trap. The pill bugs are attracted to the moisture and shelter, allowing them to be collected and relocated to a compost pile or an area where they can continue their beneficial role as decomposers.