Beneficial animals Beneficial insects Gardening

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.

Woodlouse rolled in a ball, then partly open, then fully open.
Some woodlice roll up into a ball when disturbed. Photo: biol326.wordpress.com

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, spidersshrews, 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

Composite of 4 different woodlice
Insects have 6 legs; woodlice have 14. Photo: Wikipedia Commons

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?

Raising pots on pot feet will help keep woodlice populations low. Photo: gardenartisans.com

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.

Bottle of diatomaceous earth

Woodlice often live indoors in damp spots like basements and bathrooms. If so, they’re still not harmful, but are not particularly welcome, either. An application of diatomaceous earth, an organic insecticide, to cracks and fissures in damp areas should eliminate them as will regular vacuuming. If you find many them in certain spots indoors, have your home checked: they’re might be water seeping in or the presence of rotting wood. 

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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.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

5 comments on “Woodlice: Friends Not Foes

  1. They obviously love my compost heaps as they are there in their hundreds and hundreds and are most welcome.

  2. You had me itching at the title. 🙂

  3. People freak out when encountering a banana slug for the first time. They know how much damage a normal slug can do, so figure that a huge banana slug must be proportionately damaging. However, they consume only decaying detritus, so are likewise harmless to the garden.

  4. Helen Kara

    It’s not a case of them being absent from soils containing heavy metals – they can absorb and remove heavy metals from soils, so it’s their presence that leads to the absence of heavy metals in soils that were previously contaminated! 😊

    If you search “woodlice and heavy metals” you’ll find articles about this, including one with this info:-

    Pill bugs clean up soil and protect ground water from heavy metal contamination
    In case you didn’t know, most of us are picking up heavy metals from our environment.

    One very unique and highly prized quality that these crustaceans possess is their ability to safely remove heavy metals from soil. For this reason, they are an important tool for cleaning up soil contaminated with pollutants like lead, cadmium and arsenic.

    They take in heavy metals like lead and cadmium and crystallize these ions in their guts. The heavy metal toxins are then made into spherical deposits in the mid gut. With this special cleanup property, woodlice survive where most creatures can’t, in the most contaminated sites.

    The magic of these creatures reestablish healthy soil and prevents toxic metal ions from leaching into the groundwater. This means pill bugs are also protecting well water from becoming contaminated while stabilizing soils.

    Source: https://www.naturalnews.com/

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