What Do Woodlice Eat? Their Diet and What They Avoid

Woodlice are primarily decomposers that feed on decaying plant material, especially leaf litter that has already been colonized by fungi and bacteria. Their diet is far more specific than “anything rotting on the ground,” though. These small crustaceans show strong preferences for certain types of decaying matter and actively avoid others, using chemical senses to steer clear of foods laced with toxins or heavy metals. They can also surprise you: under the right conditions, woodlice will eat living plants, graze on lichens, and even turn cannibalistic.

Rotting Leaves Are the Staple

If you had to sum up the woodlouse diet in two words, it would be “old leaves.” Dead leaf litter on the forest floor, in garden beds, or under logs makes up the bulk of what most woodlice species consume. But they are picky about which dead leaves they eat. Research consistently shows that woodlice strongly prefer leaf litter that has already been broken down by microorganisms over freshly fallen leaves. A global analysis of detritivore feeding found that microbial conditioning of litter dramatically increased consumption rates, and that woodlice and millipedes may eat little or no freshly fallen leaf material when microbially conditioned litter is available.¹

This makes intuitive sense. Freshly dropped leaves still contain high concentrations of defensive chemicals like tannins and lignin. Once fungi and bacteria get to work on them, those compounds break down, the leaf tissue softens, and the microbial colonies themselves become an additional food source. Woodlice are essentially waiting for the microbes to do the hard work of pre-digesting the toughest material before they move in. The fungi and bacteria coating a decaying leaf aren’t just tolerated by woodlice; they are a significant part of the meal.

How They Digest Such Tough Material

Even pre-softened leaf litter is full of cellulose and lignin, the structural compounds that make plant cell walls rigid. Digesting these is a challenge that most animals cannot handle alone. Woodlice solve this through a partnership between their own digestive enzymes and the microbes living in their gut. Research on the common pill bug (Armadillidium vulgare) found that both the host animal and its gut microbiome produce complementary sets of enzymes for breaking down lignocellulose, with the host’s own enzyme genes being actively expressed in digestive tissues.² The woodlouse contributes some of the biochemical machinery, its gut bacteria contribute the rest, and together they can extract nutrients from material that would otherwise pass through undigested.

This dual-enzyme system helps explain why woodlice are so ecologically important. They are among the primary shredders of leaf litter in many habitats, physically fragmenting decaying vegetation into smaller pieces that soil microbes and other organisms can process further. Without animals like woodlice doing this work, dead plant material would accumulate and decompose far more slowly.

What Woodlice Prefer and What They Refuse

Within the general category of “decaying plant matter,” woodlice have clear preferences. Studies on vine leaf decomposition found that woodlice consumed and assimilated more from litter that was lowest in tannin, lignin, and copper content.³ That trio of chemical traits forms a useful shorthand for what woodlice avoid:

• Tannins: These plant-produced compounds bind to proteins and make tissue harder to digest. Leaf litter high in tannins is consistently eaten less.
• Lignin: The compound that makes wood woody. High-lignin leaves are physically tougher and yield fewer nutrients per bite, so woodlice leave them for later stages of decomposition.
• Copper and other heavy metals: Woodlice can detect copper contamination in food through contact chemoreception and actively turn away from copper-rich leaf litter, even when their own bodies are copper-deficient.

The copper finding is particularly striking. You might expect a copper-starved animal to seek out copper-rich food. Instead, experiments with the rough woodlouse (Porcellio scaber) showed that both copper-fed and copper-deficient individuals preferred copper-poor leaf litter. When given a choice between extracts of clean and contaminated leaves, the animals turned significantly more often toward the clean option. Copper does increase the digestibility of leaf litter, but woodlice still avoid eating heavily contaminated food because the toxic risk apparently outweighs the nutritional benefit.⁴

Lichens, Fungi, and Other Non-Leaf Foods

Woodlice do not limit themselves to leaf litter. They graze on fungi, algae, moss, bark, and even lichens. But lichens present an interesting case because many species produce defensive chemicals to deter grazers. Research on Porcellio scaber feeding on the lichen Hypogymnia physodes found that woodlice could and did eat the lichen, but were deterred by its carbon-based secondary compounds at higher concentrations. When those compounds were experimentally removed by rinsing with a solvent, the woodlice preferred the cleaned pieces. At natural concentrations found in shade-adapted lichens (around five percent or less), woodlice tolerated the chemicals and fed without obvious avoidance.⁵

This pattern echoes how woodlice deal with leaf litter: they can eat a wide range of things, but they moderate their intake based on the chemical signals they detect. A lichen growing in deep shade with lower defenses becomes a more attractive food source than the same species growing in full sun with a higher chemical load. Woodlice are making cost-benefit calculations at every meal, even if those calculations happen through simple sensory responses rather than anything resembling conscious choice.

When Woodlice Attack Living Plants

Gardeners sometimes blame woodlice for damage to seedlings, strawberries, or young shoots, and the standard reassurance is that woodlice only eat dead material. The truth is more nuanced. Woodlice are overwhelmingly detritivores, but they can and do eat living plant tissue under certain circumstances. Research using the model plant Arabidopsis thaliana demonstrated that both Porcellio scaber and Armadillidium vulgare were attracted to seeds placed beneath living plants and were capable of feeding on intact, living plant tissue in laboratory conditions.⁶

The key factor that usually prevents this from happening is the plant’s own defense system, specifically the jasmonate signaling pathway. Jasmonates are hormones that plants produce in response to tissue damage, triggering the release of defensive compounds that make the plant unpalatable. When researchers used genetically modified plants that lacked jasmonate signaling, woodlouse feeding increased dramatically. The same pattern held in both Arabidopsis and rice, suggesting it is a general phenomenon rather than something specific to one plant species.

For gardeners, this has a practical implication. Healthy, vigorous plants with intact defense systems are rarely at risk from woodlice. But seedlings, injured plants, or already-wilting tissue lack the full chemical arsenal to repel them. If you find woodlice clustered around a damaged strawberry or a rotting stem base, they are likely feeding on tissue that was already compromised rather than having caused the initial damage. Still, once they start feeding, they can extend the damage beyond what the initial injury caused. The practical advice is to manage moisture and clear decaying plant debris from around vulnerable seedlings rather than trying to eliminate woodlice entirely, since they provide valuable decomposition services elsewhere in the garden.

Cannibalism and Meat-Eating

Woodlice are not strict vegetarians. Although their diet is overwhelmingly plant-based detritus, they are opportunistic enough to eat animal protein when the opportunity arises. Research has documented that woodlice prey on other woodlice, both members of different species and their own. Individuals that are weak, injured, or in the middle of molting (when the exoskeleton is soft and the animal is defenseless) are particularly vulnerable to being eaten by their neighbors.⁷

This cannibalistic behavior is not random cruelty. It serves nutritional purposes, providing concentrated protein and minerals that are scarce in a leaf-litter diet. Molting woodlice are often observed eating their own shed exoskeleton to reclaim the calcium carbonate stored in it, and consuming a recently molted neighbor may serve a similar mineral-recovery function. The behavior also has epidemiological consequences: it can transmit parasites like Wolbachia bacteria from one individual to another, which is how the researchers studying it originally became interested in the phenomenon.

Beyond cannibalism, woodlice will eat dead insects, animal feces, and other organic matter they encounter. They are generalist detritivores in the broadest sense, meaning “eaters of dead and decaying organic material” covers both plant and animal sources. If you keep woodlice in a terrarium or vivarium, providing a small amount of fish food flakes or dried shrimp alongside their leaf litter gives them access to protein and minerals they would otherwise obtain from occasional scavenging.

Not All Woodlice Eat the Same Things

There are thousands of woodlice species worldwide, and even among the handful of common European garden species, dietary habits differ in meaningful ways. A study comparing two species that commonly live side by side, Porcellio scaber and Oniscus asellus, found clear differences in what mattered for their feeding success. Adult P. scaber relied heavily on the microbes colonizing leaf litter: both the physical and chemical properties of the leaves and the microbial community growing on them affected how well the animals performed. Adult O. asellus, by contrast, were influenced by the leaf litter’s own characteristics but were not significantly affected by whether microbes were present on it.⁸

Juvenile woodlice of both species showed their own distinct nutritional requirements, adding another layer of complexity. This niche differentiation is likely one reason why several woodlice species can coexist in the same habitat without one outcompeting the others. They carve up the available food resources differently enough that direct competition is reduced. If you turn over a log and find three species sheltering together, they are probably not all eating exactly the same thing even though they live inches apart.

Heavy Metals and the Hepatopancreas

Woodlice have an unusual relationship with heavy metals that goes beyond simply avoiding contaminated food. Their hepatopancreas, a digestive organ roughly analogous to a combined liver and pancreas, is remarkably efficient at accumulating and storing metals like zinc, cadmium, lead, and copper. Studies of Oniscus asellus from contaminated sites found that the hepatopancreas contained at least 89 percent of the animal’s total body load of cadmium, with some specimens reaching tissue concentrations that are among the highest recorded in the soft tissues of any animal.⁹

Animals from heavily contaminated sites often had a physically larger hepatopancreas, suggesting the organ grows to accommodate the increased detoxification load. This sequestration strategy means woodlice can survive in surprisingly polluted environments, but it also means they accumulate metals through the food chain. Anything that eats woodlice (birds, shrews, spiders, frogs) may be getting a concentrated dose of whatever metals the woodlouse has been storing. This makes woodlice useful bioindicators: researchers can survey woodlouse populations to gauge soil contamination levels in an area.

The copper-avoidance behavior described earlier interacts with this storage system in an interesting way. Microbes on leaf litter actually facilitate copper absorption into the woodlouse’s body, even though the total copper uptake does not depend on the animal’s own copper status.⁴ So the microbial community that makes leaf litter more palatable and nutritious also increases the amount of copper that ends up in the woodlouse’s tissues. The animal’s behavioral avoidance of copper-contaminated food is essentially the first line of defense, with hepatopancreas storage as the backup plan for whatever gets through.

How Woodlice and Earthworms Share the Work

In most temperate garden and forest soils, woodlice share their leaf-shredding role with earthworms. The two groups process litter differently: woodlice fragment leaves into coarse pieces from the surface, while earthworms pull leaves into their burrows and mix them into the soil. Research testing whether the two groups work better together found that the answer depends on the type of litter. When feeding on alder leaves, which decompose relatively easily, woodlice and earthworms together broke down litter faster than you would expect by adding up their individual contributions. But on tougher oak leaves, the two together actually decomposed less than predicted from their separate effects.¹⁰

The likely explanation is competition. When the food is easy to process, both animals benefit from the other’s activity: earthworms mix microbe-rich soil into the litter layer, and woodlice break leaves into fragments that earthworms can handle more easily. When the food is tough and scarce, they may interfere with each other’s feeding, competing for the same limited patches of palatable material. For gardeners managing a compost system that includes both woodlice and earthworms, this suggests that providing a mix of softer, nitrogen-rich material alongside tougher brown matter lets both groups contribute most effectively without getting in each other’s way.

Feeding Woodlice in Captivity

Woodlice are increasingly popular in bioactive terrariums and as cleanup crews in reptile and amphibian enclosures. Feeding them well means mimicking the food diversity they would encounter in a healthy forest floor. The foundation should be decaying hardwood leaf litter, ideally collected and allowed to age for several weeks so microbial colonization is well underway. Oak, beech, and maple leaves all work, though oak decomposes more slowly and may be consumed less readily than softer species.

Beyond leaf litter, captive woodlice benefit from a few supplemental foods. Rotting bark and softwood provide additional cellulose sources. Dried cuttlefish bone or crushed eggshell supplies calcium carbonate, which woodlice need in large quantities to build and maintain their exoskeletons, especially during molting. A small amount of vegetable scraps like cucumber, carrot, or squash can be offered and will typically be eaten once it starts to soften and decompose. Protein can come from fish food flakes, dried mealworms, or simply from the fungi and bacteria growing on the leaf litter itself.

What to avoid in a captive setup mirrors what woodlice avoid in the wild: anything with high concentrations of aromatic compounds, essential oils, or pesticide residue. Conifer needles, eucalyptus leaves, and cedar bark are commonly cautioned against because their volatile oils can be irritating or toxic to small invertebrates. Citrus peels are another food to skip. Keeping the substrate consistently moist but not waterlogged ensures that microbial communities thrive on the leaf litter, which as we have seen is what actually makes the leaves appetizing. A bone-dry enclosure means the food source dries out and microbial activity stalls, leaving woodlice with material they are reluctant to eat.