Earthworms do have a mouth, a small opening at the very tip of the front end, though it has no teeth and no jaws. Rather than biting, a worm swallows its food, and much of what it is after is not the soil itself but the fungi and bacteria growing on rotting plant matter.1Ask Dr. Universe. Do worms eat and have mouths?
What an Earthworm’s Mouth Looks Like and How It Works
To find the mouth on a worm you’re holding, start with the clitellum, the smooth, swollen pale band that sits near one end. The mouth is on the end closer to that band, and this is usually the end that leads when the worm crawls. Over the mouth hangs a small fleshy lip, which the worm uses to probe and push into soil. The mouth opens on the underside, not straight ahead, so turn the worm gently to see it. Keep the worm moist and put it back in soil within a few minutes.
The tip holds both the mouth and sensory parts that help the worm find food.2Ask Dr. Universe. Do worms eat and have mouths? It is more sensitive than the rest of the body to tastes such as sugars and bitter substances.3Comparative Biochemistry and Physiology. Tactile and chemical perception in earthworms —I. Responses to touch, sodium chloride, quinine and sugars The two ends can look alike at a glance, so the clitellum is the most reliable landmark, but it is fully visible only on adult worms. A small pale young worm may show no band at all, which doesn’t mean it lacks a front end. The front tends to taper to a slightly more pointed tip, while the rear is often blunter or flatter.
Earthworms have no teeth, so they cannot bite or chew at the mouth. Instead, a muscular throat pumps and sucks soft food and soil into the mouth.4Ask Dr. Universe. Do worms eat and have mouths? That is why worms favour food that is already soft and rotting, such as moist dead leaves.
A common mistake is thinking worms have no mouth, or that they eat through their skin. Worms do breathe through their moist skin, which is why people assume they absorb food that way too. But food enters only through the mouth and travels down one tube to the rear opening.
What Earthworms Eat
Earthworms slurp up bacteria, fungi and decaying matter along with soil.5Ask Dr. Universe. Do worms eat and have mouths? Given a choice, they pick certain soil fungi over others, and different worm species share very similar tastes.6Pedobiologia. Food preferences of earthworms for soil fungi Fast-growing fungi and some fungi that cause plant disease are among their favourites.7Pedobiologia. Food preferences of earthworms for soil fungi The tough fungi that rot wood, the kind that form bracket shelves on trees, are mostly avoided.8Pedobiologia. Food preferences of earthworms for soil fungi
Worms swallow a lot of soil, but most mineral grains pass through with little change, so the soil works mainly as a carrier. The valuable part is the thin film of fungi, bacteria and bits of dead plant stuck to soil and leaf surfaces.
Freshness matters too. On decaying straw, worms prefer the early-stage fungi that feed on sugars and soft plant fibre, and they pass over the fungi that break down the woody, tougher parts typical of late decay.9Soil Biology and Biochemistry. Selective consumption of decomposing wheat straw by earthworms
A fresh, dry or tough leaf is hard for a toothless worm to take in, so it often sits for days or weeks before worms touch it. As microbes colonise and soften the leaf, it becomes both easier to swallow and more nourishing.
In a garden or compost bin, this means soft vegetable scraps and fallen leaves suit worms better than sticks or woodchips. Letting scraps sit a few days gives fungi and bacteria time to grow, and that growth is the actual meal. A layer of leaves on the soil gives a steady food supply, and moisture matters because worms can only swallow soft, wet food.
Garden earthworms eat mainly dead and decaying matter rather than healthy living roots. If roots are being damaged, other pests such as grubs are the usual cause.
How Earthworms Grind and Digest Food
After the throat, food passes down a narrow tube into a storage pouch called the crop. Next comes the gizzard, a thick muscular pouch that squeezes food against swallowed grit. Grinding in the gizzard and gut turns soil and leaf bits into fine particles, and smaller pieces give digestive microbes more surface to work on.10IOP Conference Series: Earth and Environmental Science. The earthworm gastrointestinal effect on the release of organic bound residues in soils
With no teeth, a worm relies on small mineral particles it has swallowed, which act like tiny grinding stones inside the gizzard. The grit arrives automatically with each meal because the worm eats soil along with its food. The long intestine then absorbs nutrients with help from enzymes and bacteria, and the leftovers leave from the rear opening as casts.
The worm’s gut has strong activity of enzymes that break down cellulose, the tough fibre in plant cell walls, and very little activity of fat-digesting enzymes.11Revista de Biología Tropical. Microbial diversity and digestive enzyme activities in the gut of earthworms found in sawmill industries in Abeokuta, Nigeria Part of that comes from the worm itself: earthworms can make their own cellulose-digesting enzyme near the front of the gut.12Soil Biology and Biochemistry. The contribution of endogenous cellulase to the cellulose digestion in the gut of earthworm (Pheretima hilgendorfi: Megascolecidae) Some worms also make powerful protein-digesting enzymes, stronger and more stable than the one in the human gut.13Journal of Molecular Catalysis B: Enzymatic. Earthworm-serine protease: characterization, molecular cloning, and application of the catalytic functions
Gut bacteria finish the job. Bacteria in the worm’s gut help digest cellulose and other complex carbon foods.14PubMed. Gut microbial communities and their potential roles in cellulose digestion and thermal adaptation of earthworms15PubMed Central. Bacterial Keystone Taxa Regulate Carbon Metabolism in the Earthworm Gut Worms whose gut bacteria were removed broke down cellulose most slowly, about 1% in one test.16PubMed. Gut microbial communities and their potential roles in cellulose digestion and thermal adaptation of earthworms Bacteria from a worm’s own gut also break down cellulose faster than bacteria from elsewhere.17PubMed. Gut microbial communities and their potential roles in cellulose digestion and thermal adaptation of earthworms
Many leaves contain bitter chemicals that can glue up digestive proteins. Earthworms get around this by making special soap-like molecules that protect their gut proteins from these chemicals.18PubMed Central. Ecological adaptation of earthworms for coping with plant polyphenols, heavy metals, and microplastics in the soil: A review Unlike man-made detergents, these molecules do this without weakening the worm’s digestive enzymes.19PubMed Central. Unique metabolites protect earthworms against plant polyphenols
How Earthworms Find Food Without Eyes
A worm cannot see a meal, so it relies on touch, taste and smell. The whole body surface responds to touch and to salt.20Comparative Biochemistry and Physiology. Tactile and chemical perception in earthworms —I. Responses to touch, sodium chloride, quinine and sugars Worms get used to touch quickly, but they stay sensitive to salt much longer.21Comparative Biochemistry and Physiology. Tactile and chemical perception in earthworms —I. Responses to touch, sodium chloride, quinine and sugars That is why salt hurts them: it triggers a response across the entire body, and because they adapt slowly, the irritation lasts.
Fine taste detection is concentrated at the front tip, where food is first met. Taste sensors for sugars, glycerol and bitter quinine sit mainly there.22Comparative Biochemistry and Physiology. Tactile and chemical perception in earthworms —I. Responses to touch, sodium chloride, quinine and sugars
Worms can also follow smells in soil to locate patches of microbes they feed on.23PubMed Central. Earthworms Use Odor Cues to Locate and Feed on Microorganisms in Soil They have chemical sensors on the lip and mouth lining linked to their nerves.24PubMed Central. Earthworms Use Odor Cues to Locate and Feed on Microorganisms in Soil
Worm Casts and What They Do for Soil
The small soil piles worms leave behind are called casts, essentially worm droppings. On average they hold about 241% more plant-usable nitrogen and 84% more usable phosphorus than nearby soil.25Geoderma. How fertile are earthworm casts? A meta-analysis Digestion changes nutrients into forms plants can take up.26Geoderma. How fertile are earthworm casts? A meta-analysis
Casts are also hotspots of microbes and enzyme activity,27Plant, Soil and Environment. Chemical composition of earthworm casts as a tool in understanding the earthworm contribution to ecosystem sustainability – a review and these keep working after the cast is deposited, continuing to release nutrients. Their makeup varies with both the worm species and the soil type,28Applied Soil Ecology. The interactions between soil type and earthworm species determine the properties of earthworm casts so results differ between gardens.
Digestion also filters some germs. Passing through a worm’s gut reduced or removed many human-linked bacteria in sewage sludge, but a few types became more common after gut transit.29PubMed Central. Effect of Earthworm Digestion on Abundance, Composition and Diversity of Bacterial Pathogens in Sewage Sludge from Wastewater Treatment Plants The front gut breaks up active soil protozoa, though their tough resting forms pass through intact.30Pedobiologia. Fate of protozoa transiting the digestive tract of the earthworm Lumbricus terrestris L. Worm-processed material is therefore not automatically germ-free.
Different Worms, Different Diets
Earthworms fall roughly into three feeding styles:
- Surface dwellers: live in leaf litter and eat decaying leaves with little or no soil.31Soil Biology and Biochemistry. Earthworm δ13C and δ15N analyses suggest that putative functional classifications of earthworms are site-specific and may also indicate habitat diversity
- Soil dwellers: live in the soil and eat mostly earth and the organic matter mixed into it.32Soil Biology and Biochemistry. Earthworm δ13C and δ15N analyses suggest that putative functional classifications of earthworms are site-specific and may also indicate habitat diversity
- Deep burrowers: make long-lasting vertical burrows and pull surface litter down to eat.33Soil Biology and Biochemistry. Earthworm δ13C and δ15N analyses suggest that putative functional classifications of earthworms are site-specific and may also indicate habitat diversity
The red worms in compost bins are surface dwellers that thrive on scraps, which is why they suit a bin, unlike deep burrowers, which need soil depth. The large nightcrawlers that come up after rain are deep burrowers. Pale or greyish worms in dug soil are often, though not always, soil dwellers.
These habits shape what each worm does to the ground. Surface worms mainly shred and break down leaf litter and tend to stay near the top. Soil dwellers mix and process the earth itself, so their casts reshape the soil’s structure. Deep burrowers connect the surface and the depths, hauling litter down and opening channels that water and roots can use.
The groups blur together. Soil dwellers eat more heavily processed organic matter, while surface and burrowing worms prefer fresher material.34Rapid Communications in Mass Spectrometry. A Dynamic Study of Earthworm Feeding Ecology Using Stable Isotopes Diets form a sliding scale from leaf eaters to processed-soil eaters rather than neat boxes,35Applied Soil Ecology. Ecological groups and isotopic niches of earthworms and worms in the same group can still split up food sources between them.36Applied Soil Ecology. Ecological groups and isotopic niches of earthworms
When Earthworm Feeding Harms Soil
Many northern North American forests had no earthworms after the last ice age, and introduced worms now spread there. Trees in these forests grew up with a thick, spongy layer of leaves that decays slowly, and worms eat through it far faster than the forest is used to. In one maple forest, soil carbon was 37% lower where worms had invaded, mainly because they ate away the leaf layer on the forest floor.37PubMed. Earthworm effects on the incorporation of litter C and N into soil organic matter in a sugar maple forest Across studies, invaded soils became drier and less acidic.38PubMed Central. Soil chemistry turned upside down: a meta-analysis of invasive earthworm effects on soil chemical properties Once the layer is gone, the bare soil beneath is more exposed. Wildflowers, tree seedlings and small animals that rely on the leaf layer for moisture, cover or food can lose their habitat as it thins.
On farms, the effect depends on management. In a low-input farm system, worms increased the new carbon locked into soil crumbs by 35%.39Soil Biology and Biochemistry. Influence of earthworm activity on aggregate-associated carbon and nitrogen dynamics differs with agroecosystem management In a conventional system, worms seemed to reduce new nitrogen stored in soil.40Soil Biology and Biochemistry. Influence of earthworm activity on aggregate-associated carbon and nitrogen dynamics differs with agroecosystem management
If you live near a worm-free forest, don’t dump leftover fishing bait worms in the woods. Buy mulch and compost from sources that check for invasive worms, and clean soil from boots and tires before hiking into wild forests. In gardens, earthworms remain generally helpful.