Woodlice: Friends Not Foes

Photo: Katia Schulz, Wikipedia Commons

You find them in almost every garden: flat, oval, usually gray creatures no more than 1/2 inch (1 cm) long, with a segmented exoskeleton and 14 legs. There are over 3,500 species worldwide and probably half a dozen or so in your own garden. Some can roll up into a ball for protection and may be called pill bugs or roly-polies, but not all can perform that little trick. They have dozens of other common names—slater, potato bug, sow bug, wood bug, etc.—but I’ll use woodlice (singular: woodlouse) here.

A lot of people have a natural aversion to woodlice, as to other creepy-crawlies, but they are in fact harmless to people. And, for the most part, they’re beneficial in the garden. They’re essentially detritivores: they consume and decompose dead plant matter, fungi and other litter, turning it into a form plants can absorb. They also aerate the soil. They’re often abundant in compost, logically enough, and, being largely nocturnal, hide out under mulch, logs and rocks during the day. They also form part of the garden’s food web, feeding birds, spiders, shrews, toads, centipedes, ground beetles and other garden predators. Birds find them especially beneficial, as the carapace of woodlice is rich in calcium, an element birds need to form their eggs.

On the Downside

Woodlice have been known to occasionally damage seedlings, although I’ve personally never experienced that, but they do nibble on ripe strawberries. (One of the reasons straw is often used as a mulch for strawberries is that it’s a light, airy mulch not conducive to woodlice.) They are sometimes blamed for attacking other, tougher plant parts, but usually it turns out slugs, snails or earwigs did the initial damage and the woodlice are just there to clean up.

Woodlice are often considered bioindicators of a healthy environment. In other words, if you don’t find them in your garden, maybe you need to worry. For example, they may be absent from soils rich in heavy metals such as zinc, cadmium and lead. 

Not Insects

Most gardeners probably think of woodlice as being insects, but in fact, they are crustaceans, related to lobsters and crabs, and belong to a branch of the family called isopods. Originally aquatic, they left the ocean millions of years ago, although some species are still aquatic or semi-aquatic, including the giant isopods found in the depths of the ocean. Terrestrial woodlice still need a thin coating of water on their legs (where their lungs are) in order to breathe, which is why they hang out in damp places and avoid dry spots and bright sun.

The mother woodlouse carries her eggs and later her young in a pouch under her abdomen like a marsupial. There can be several generations per year, depending on the species, and the young shed their exoskeleton several times as they grow. They can live for 2 to 4 years.

What to Do About Woodlice?

In most cases, nothing. Live and let live. Remember, they’re good for the garden and the plants that grow there. If you’re finding too many of them hiding under pots in the garden, raise them on pot feet, creating an airier environment, and the woodlice will move elsewhere. 

Before you bring plants back indoors in the fall, soak their pot in soapy water for 15 minutes or so to get rid of any unwanted travelers, including woodlice.

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Woodlice: they aren’t particularly loveable, but are mostly beneficial and a good gardener will learn to just let them be.