Pillbugs and Sowbugs: Friend, Foe, or Just Garden Background?

You flip over a pot and they scatter in every direction, or roll into perfect little gray spheres and wait you out. Pillbugs. Roly polies. That first bug most of us ever picked up as kids. Here in the PNW, you will find them absolutely everywhere: under every board, lining the bottoms of raised bed frames, tucked into compost piles by the hundreds. And every year, gardeners wonder the same thing: are these things hurting my plants?

The short answer is almost certainly not. But the longer answer is worth knowing, because understanding what pillbugs and sowbugs actually do in your garden changes how you see them.

What Are Pillbugs and Sowbugs, Exactly?

Before anything else, here is the fact that surprises nearly everyone: pillbugs and sowbugs are not insects. They are terrestrial crustaceans in the order Isopoda, which puts them in the same evolutionary family as crabs, shrimp, and lobsters. They just happen to be the branch that moved onto land. A pillbug has more in common with a crayfish than with a beetle.

Both species have seven pairs of legs and segmented, plate-like bodies that typically measure between one-third and three-quarters of an inch long. In the garden, you will most often encounter two species: Armadillidium vulgare (the pillbug) and Porcellio scaber (the sowbug). They look similar at a glance, but they behave differently when startled, which is the easiest way to tell them apart.

Pillbug vs. Sowbug: How to Tell Them Apart

The classic test is to give them a gentle nudge. A pillbug rolls into a tight, smooth ball and stays put. That defensive curl is the origin of the name "roly poly," and it is the defining characteristic of Armadillidium vulgare. A sowbug cannot roll up. Instead, it flattens itself and makes a run for the nearest shadow. Sowbugs also have two small tail-like appendages at their rear end, which pillbugs lack. Both are gray to slate-brown, both are completely harmless to handle, and both are doing the same job in your garden.

Why They Need Moisture to Breathe

Unlike insects, pillbugs and sowbugs still breathe through gill-like structures. This means they need moisture to survive, which is why they cluster under pots, logs, mulch, and any debris that holds humidity. In the PNW's cool, wet climate they can range more freely and stay active nearly year-round. During a hot dry spell, you will find them concentrated in the dampest spots available. That moisture dependence is also why PNW gardens tend to have especially large populations: our climate is genuinely ideal for them.

The Roly Poly Life Cycle (and Why Your Garden Is Perfect for Them)

Females carry their eggs inside their bodies until they hatch, then hold the young (called mancas) in a brood pouch before the juveniles disperse on their own. Pillbugs typically become adults by late summer and overwinter before reproducing in their second year. A single population can persist in the same garden bed for years with no intervention, generation after generation turning over quietly under your mulch.

In zone 9a coastal gardens, the conditions that make our beds so productive also create ideal isopod habitat: consistent moisture, abundant organic matter from heavy mulching practices, mild winters that allow year-round activity, and rich, biologically active soil. High populations are not a warning sign here. They are confirmation that your garden soil is doing what it should. A garden thriving with pillbugs is a garden with a healthy decomposer community at work.

What Do Pillbugs Eat? (Mostly Your Mulch)

Pillbugs and sowbugs are primary decomposers. Their preferred foods are decaying plant material, fungi, and dead organic matter: fallen leaves, rotting wood, spent mulch, compost scraps. They are essentially a cleanup crew for material that is already dying or dead. UC IPM notes that pillbugs and sowbugs "feed primarily on decaying plant material and are important decomposers of organic matter," returning nutrients to the soil in a form plants can use.

They are not hunters. They are not chasing down your healthy broccoli transplants. Healthy green plant tissue is not particularly attractive to them as long as there is rotting material available, which in a PNW garden there almost always is.

When They Actually Become a Problem

The exceptions are real but narrow. Pillbugs and sowbugs will occasionally feed on very soft plant tissue when succulent material is in direct contact with moist soil. The specific scenarios where damage actually occurs: young seedlings with soft stems at soil level, ripe strawberries lying directly on the ground, and overripe tomatoes or other fruit that has fallen and is beginning to soften. The Royal Horticultural Society confirms this: woodlice "occasionally damage very soft plant tissues, such as seedlings and sometimes strawberry fruits," but holes found in mature established plant material are typically the work of slugs or caterpillars, not isopods.

If you see ragged holes in your tomatoes, kale, or mature lettuce and you are blaming pillbugs, look more carefully for slug trails. Slugs are the far more likely culprit in a PNW garden, and the damage patterns look similar enough to cause real confusion.

The Friend Case: Why Pillbugs and Sowbugs Are Usually Good News

When pillbugs eat dead organic matter, they fragment it into smaller pieces that bacteria and fungi can break down faster. This accelerates nutrient cycling and helps build the spongy, aggregated soil structure that PNW gardeners work hard to achieve. In your compost pile, they are active contributors, speeding the conversion of raw scraps into finished compost. Under your raised bed's wood frame, they are quietly processing the debris that accumulates there into something the bed's soil can absorb.

They also feed the food chain. Shrews, toads, and ground beetles all eat pillbugs and sowbugs. If you have a garden that attracts any of these beneficial predators, the isopod population is part of what's sustaining them. The RHS recommends no control measures for woodlice and explicitly frames them as a vital part of garden biodiversity.

And there is something worth saying about the non-scientific case: the roly poly is most people's first wild creature. A kid who learned to trust the curled gray ball in their palm is a kid who grew up comfortable with the living world. That experience matters, and it starts with understanding that this small armored creature is not an enemy.

The (Rare) Foe Scenarios: When to Actually Do Something

The threshold for intervention is simple: only act if you observe active feeding damage on a vulnerable plant. Seeing pillbugs in the vicinity of a plant is not evidence of damage. Finding actual holes or tissue loss on a seedling stem or a strawberry, while pillbugs are present and clearly feeding, is.

Protecting Seedlings

Seedlings with tender stems at or below soil level are the main vulnerability. If you are starting seeds directly in garden beds and have a confirmed history of seedling damage, a thin ring of diatomaceous earth around the base of individual seedlings can create a temporary physical barrier. Use it as a targeted tool around specific at-risk plants only, not broadcast across the bed. Broad DE applications harm a wide range of beneficial soil organisms, and in a thriving PNW garden, that tradeoff is rarely worth it. The goal is to protect the seedling through its most vulnerable week or two, not to eliminate the population.

Reducing the amount of mulch piled directly against seedling stems also helps. Pull mulch back a few inches from stems to reduce the humid microhabitat right at the soil-stem junction.

Protecting Low-Hanging Fruit

For strawberries, the most effective control is also the simplest: get the fruit off the soil. Strawberry mats, straw mulch raised under developing berries, or drip-irrigated raised beds all reduce contact between ripe fruit and moist ground. Harvest strawberries promptly when ripe rather than letting them sit. For tomatoes, pick up fallen fruit as soon as you notice it. A tomato that fell yesterday and is beginning to soften is a pillbug invitation; a garden where fallen fruit is cleared regularly rarely has problems.

How to Reduce Pillbug Populations If You Need To

In genuinely problematic situations, the most effective controls work by making the environment less hospitable rather than by killing individual insects. UC IPM's guidance centers on habitat reduction: let the soil surface dry between waterings where possible, switch from overhead irrigation to drip, pull mulch away from plant stems, and remove debris piles near beds. These changes reduce the moist microhabitats that sustain large populations near vulnerable plants.

Practical steps worth trying first:

• Pull mulch back from seedling stems by a few inches to reduce moisture at the soil-stem junction.
• Elevate strawberry fruit off the soil using straw, plastic mulch, or berry mats.
• Pick up fallen fruit promptly so softening produce does not attract feeding activity.
• Harvest ripe vegetables daily during peak season, particularly anything resting on the soil.
• Use a targeted DE ring around individual seedlings only, not as a broadcast treatment.
• Hand-pick at night with a flashlight if populations around specific plants are high; drop into soapy water.

You do not need pesticides for pillbugs. Broad-spectrum soil insecticides kill the beneficial organisms doing the same decomposition work and disrupt the food web that keeps your garden healthy. No chemical intervention is recommended or necessary for typical pillbug populations.

Living With Pillbugs and Sowbugs in the PNW Garden

Here is the honest reality for gardeners in coastal Oregon and Washington: you will always have pillbugs and sowbugs. Our climate is essentially their paradise. Under every pot, in every compost bin, beneath every raised bed frame, they are there, and they have been doing this work in gardens long before we showed up with our raised beds and drip lines.

The same cool, moist, organic-rich conditions that make PNW vegetable gardens so productive also sustain thriving isopod populations. Finding a hundred pillbugs under a stepping stone is not a crisis. It is a normal snapshot of a biologically active soil ecosystem doing its job.

If there is no damage to your plants, there is nothing to manage. Let them roll. Let them flatten and scatter. They are breaking down your mulch, feeding your soil food web, and providing prey for the toads and shrews that help keep your garden in balance. The roly poly that delighted you as a kid is doing exactly the same thing in your garden right now. That is worth appreciating.

Seeing actual plant damage from soil-dwelling pests? In the PNW, slugs and snails are the far more common culprit. And if you find something that looks like a pillbug but has pincers at the rear, check out our guide to earwigs in the garden for another surprisingly nuanced friend-or-foe story.