Pillbugs, commonly known as “Rolly Pollies” or woodlice, are not insects but terrestrial crustaceans (isopods) related to shrimp and lobsters. This small, segmented creature is famous for its defensive behavior of rolling into a tight, armored ball, a process called conglobation. Pillbugs are found in nearly all temperate ecosystems worldwide, typically living in dark, moist environments like under logs, rocks, or leaf litter. Their feeding habits are a fundamental process in maintaining soil health.
The Primary Diet: Detritus and Decay
Pillbugs are detritivores, focusing almost exclusively on consuming dead and decaying organic matter (detritus). Their preferred food sources include rotting leaves, soft decaying grasses, and decomposing wood fibers. They break down tough organic materials that other soil organisms cannot immediately process. Pillbugs also consume fungi, which helps regulate the release of carbon dioxide from the soil into the atmosphere.
They exhibit coprophagy, or consuming their own feces, which helps them retain copper and other necessary trace minerals. They are frequently found in areas with high organic debris, such as compost piles or under mulch. As terrestrial crustaceans, they breathe through gills and must remain in damp environments to prevent desiccation, making decomposing matter their ideal habitat.
Essential Role in Soil Health
Pillbugs act as primary decomposers by consuming detritus, performing a foundational service in the ecosystem. Their feeding habits break down large pieces of complex organic material into smaller fragments, significantly accelerating the rate of decomposition. This mechanical breakdown makes the organic matter more accessible to smaller organisms like bacteria and fungi, which complete the decay process.
This process is directly tied to nutrient cycling, as the consumption and excretion of waste returns sequestered nutrients back into the soil. They help release compounds containing nitrogen, phosphorus, and carbon back into the soil structure, which plants can then absorb for growth. Furthermore, pillbugs absorb and crystallize heavy metals like lead, cadmium, and arsenic in their midgut, effectively removing them from the soil and preventing leaching into the groundwater.
Addressing the Garden Pest Question
The pillbug’s primary diet of dead matter means they are generally considered beneficial recyclers, but they can occasionally become a nuisance in a garden setting. They are not true plant pests, as they do not actively seek out healthy, firm plant tissue like slugs or caterpillars. However, if the population is extremely large and their preferred food sources are scarce, they may resort to eating tender live plants.
This secondary feeding damage most often occurs on plant parts that are already soft, damaged, or resting directly on damp soil. Examples of this damage include nibbling on the soft tissue of young seedlings, the lower leaves of plants near the ground, or moist fruits like strawberries that are in contact with the soil. Damage is concentrated at the soil level and usually happens at night, when the pillbugs are most active.