Pill bugs and sow bugs look nearly identical at first glance, but there’s one quick way to tell them apart: pick one up. If it rolls into a tight ball, it’s a pill bug. If it can’t roll up and you notice two small tail-like projections at its rear end, it’s a sow bug. Both are terrestrial crustaceans, not insects, and they share similar habitats, diets, and moisture needs. But they belong to different families and have distinct physical features once you know where to look.
How to Tell Them Apart
The fastest identification method is the roll test. Pill bugs curl into a near-perfect sphere when disturbed, tucking their legs and antennae inside so no appendages are visible. This ability, called conglobation, serves double duty: it protects them from predators and helps them retain moisture by sealing off their soft underside.
Sow bugs simply cannot do this. Their body shape and segment structure don’t allow it. Instead, sow bugs have two small tail-like appendages called uropods that stick out from their last body segment. These are easy to spot if you look at the rear end of the animal. Pill bugs lack any visible rear projections.
Body shape offers another clue. Sow bugs tend to be slightly flatter and more oval, while pill bugs are rounder and more domed in profile. The most common sow bug species has a rough, bumpy body surface and is typically grey or deep blue, though orange specimens exist. It grows up to about 17 mm long (a little over half an inch). Pill bugs are similar in size and color range but have a smoother, more rounded appearance.
What They Actually Are
Neither pill bugs nor sow bugs are bugs at all. They’re isopods, a group of crustaceans more closely related to shrimp and crabs than to any insect. They’re the only crustaceans that have fully adapted to life on land, though “fully” is generous: they still breathe through gill-like structures and are completely dependent on moisture to survive. This is why you find them in damp, dark places and almost never out in the open during the day.
Pill bugs belong to the family Armadillidiidae, with the most common species being Armadillidium vulgare (sometimes called the common roly-poly). Sow bugs belong to a separate family, Porcellionidae, with Porcellio scaber (the rough woodlouse) being the species you’re most likely to encounter in North America and Europe. Despite the different family names, their lifestyles overlap almost entirely.
Where You’ll Find Them
Both species are nocturnal and spend daylight hours hiding in moist microhabitats: under rocks, logs, leaf litter, mulch beds, flower pots, and landscape timbers. They gravitate toward any spot where soil stays damp and organic material is decaying. This is their primary food source, and it’s also what keeps them alive, since dry air can kill them within hours.
That moisture dependence is what sometimes drives them indoors. Crawl spaces, basements, and ground-level floors can attract both pill bugs and sow bugs during dry spells or when outdoor conditions shift. The good news is that homes are generally too dry for them. Without sustained high humidity, they dehydrate and die quickly inside a house. An indoor sighting usually means there’s a moisture problem near your foundation rather than a true infestation.
What They Eat
Both pill bugs and sow bugs are detritivores, meaning they feed primarily on decaying plant material. Fallen leaves, rotting wood, decomposing mulch, and dead roots make up the bulk of their diet. In this role, they’re genuinely beneficial. They break down organic matter and return nutrients to the soil, functioning as a small but steady composting crew.
They also help clean up contaminated soil. Terrestrial isopods absorb heavy metals like copper, cadmium, lead, and zinc from the soil and leaf litter they consume. Researchers have even used isopod tissue to measure the degree of metal contamination in a given area. The metals accumulate in their bodies primarily through digestion, since they eat leaf litter more than any other food source, and leaf litter can concentrate metals from the surrounding environment.
The downside for gardeners is that both species will chew on living plants when conditions are right. Seedlings, strawberries, and other fruit or vegetables resting on damp soil are vulnerable, along with succulent plant parts and young transplants. The damage is usually minor compared to slugs or other pests, but it can be frustrating in a vegetable garden.
Managing Them Around Your Home
Pill bugs and sow bugs rarely need active control. When they do become a nuisance, the most effective approach targets their moisture and shelter needs rather than the animals themselves.
- Remove harborage near your foundation. Pull back leaf litter, mulch, stacked lumber, rocks, and dense ground cover from the perimeter of your house. Elevate planters and flower pots so air circulates beneath them. Check thick braided doormats, which can trap moisture underneath.
- Reduce indoor moisture. Ventilate basements and crawl spaces. Fix leaky pipes and improve drainage around your foundation. Without humidity, these animals cannot survive indoors.
- Seal entry points. Make sure windows and doors fit tightly, and seal cracks or gaps in your foundation walls.
- Adjust garden watering. Overwatering creates ideal isopod habitat. Let garden beds dry between waterings and remove excess dead plant material that provides both food and shelter.
If you find them indoors, a vacuum or broom is all you need. Pesticides aren’t recommended inside because the animals will die on their own from desiccation. For outdoor situations where they’re damaging garden plants, confirm they’re actually the culprit before treating. Go out at night with a flashlight to see whether isopods or something else is feeding on your plants. Contact insecticides and baits labeled for these species are effective when applied to mulched areas and hiding spots, but removing their preferred habitat is a longer-lasting solution.
Quick Comparison
- Rolling ability: Pill bugs roll into a ball. Sow bugs cannot.
- Tail appendages: Sow bugs have two visible uropods. Pill bugs have none.
- Body shape: Pill bugs are rounder and more domed. Sow bugs are flatter and more oval.
- Body texture: Common sow bugs have a rough, bumpy surface. Pill bugs tend to be smoother.
- Diet, habitat, and moisture needs: Essentially identical between the two.
From a practical standpoint, the distinction between pill bugs and sow bugs matters mostly for identification. Their behavior, diet, habitat preferences, and management are the same. If you’re finding small grey crustaceans under your flower pots, the approach is identical regardless of which one you’re dealing with.