Dogs eat earthworms mostly because worms smell and taste interesting to them. The behavior is driven by curiosity, scent attraction, and natural scavenging instincts rather than any single nutritional deficiency. While the habit is common and usually harmless in the moment, earthworms can carry parasites and concentrated soil toxins that pose real health risks over time.
Scent, Texture, and Instinct
To your dog’s nose, an earthworm is a rich, complex scent profile wriggling on the ground. Dogs process the world primarily through smell, and the strong earthy odor of a live or decaying worm is genuinely stimulating for them. The texture and movement add to the appeal. Think of it less as a dietary choice and more as sensory exploration, the canine equivalent of picking up something interesting to examine it, except dogs examine things with their mouths.
There’s also an ancestral component. Wolves and wild canids are opportunistic scavengers that eat insects, grubs, and small invertebrates when they encounter them. Your dog hasn’t lost that programming. The impulse to snap up a small, slow-moving creature on the ground is deeply wired. Some dogs also seem to simply enjoy the act. The same instinct that drives dogs to roll in strong-smelling substances (a behavior linked to scent camouflage and communication in wild canids) can drive them to mouth or eat things with potent odors.
Is It a Nutritional Deficiency?
This is the first thing most owners wonder, but the evidence is thin. There’s no solid research linking earthworm eating to a specific missing nutrient. Experts at the AKC note that the same debate applies to grass eating: some suggest a nutritional gap, others point to digestive self-soothing, and others believe dogs just like the taste. The honest answer is that most dogs who eat earthworms are well-fed and nutritionally complete. If your dog’s diet is balanced and they’re maintaining a healthy weight, a deficiency is unlikely to be the driver.
That said, dogs with pica (the compulsive eating of non-food items) may target earthworms along with dirt, rocks, or other objects. Pica can stem from gastrointestinal discomfort, anxiety, boredom, or in some cases genuine nutritional issues. If your dog obsessively seeks out and consumes earthworms or other non-food items on every walk, that pattern is worth investigating. An occasional worm grab on a rainy day is normal dog behavior. Compulsive, repeated consumption of odd items is different.
The Real Risk: Parasites
Earthworms serve as intermediate hosts for several parasites that can infect dogs. This is the most concrete reason to discourage the habit.
- Lungworm: Earthworms ingest lungworm eggs from contaminated soil. The eggs hatch inside the worm, and when your dog eats that earthworm, infective larvae travel to the lungs. Lungworm infections can cause coughing, breathing difficulty, and exercise intolerance.
- Giant kidney worm: According to the CDC, aquatic oligochaete worms (close relatives of common earthworms) act as intermediate hosts for this parasite. It’s rare in domestic dogs but serious when it occurs, as the worm lodges in the kidney and can cause severe organ damage.
Most healthy dogs on regular parasite prevention won’t develop a full-blown infection from a single earthworm. But dogs who frequently eat worms, especially in areas with wildlife that shed parasite eggs into the soil, face higher cumulative exposure. Signs of a parasitic infection from this route include coughing, weight loss, decreased appetite, vomiting, and dark or bloody stool. Some infections show no symptoms at all until they’re advanced.
Chemical Contamination in Soil
Beyond parasites, earthworms are remarkably efficient at absorbing and concentrating whatever is in the soil around them. Research published in Cogent Environmental Science identifies heavy metals and pesticides as the primary toxins that bioaccumulate in earthworm tissue. The metals most commonly found in earthworm bodies include lead, cadmium, mercury, aluminum, and arsenic, all of which the World Health Organization lists among the most dangerous environmental pollutants.
Pesticides are equally concerning. In documented cases involving birds, earthworms served as the direct transmission route for insecticides like carbofuran and diazinon, causing deaths in wild bird populations in Canada. Neonicotinoid insecticides, widely used on lawns and in agriculture, also accumulate in earthworms. Even botulinum toxin has been identified in earthworms living in contaminated soils. A dog eating one or two worms from a clean backyard faces minimal chemical risk, but a dog regularly eating worms from treated lawns, golf courses, agricultural edges, or urban soils could be ingesting concentrated doses of whatever chemicals have been applied or deposited there.
How to Reduce the Behavior
You’re unlikely to completely eliminate a dog’s interest in earthworms, but you can manage the behavior effectively. The most reliable approach is a strong “leave it” or “drop it” command, practiced first with low-value distractions and gradually worked up to high-value temptations like worms on a rainy sidewalk. Reward the moment your dog looks away from the worm rather than waiting until they’ve already picked it up.
Timing matters too. Earthworms surface after rain and in the early morning when soil is damp, so those are your highest-risk windows. Keeping your dog on a shorter leash during post-rain walks gives you more control. If your dog hunts for worms in your own yard, reducing overwatering and clearing worm-heavy areas before letting your dog out can help. For dogs who eat worms compulsively, increasing physical exercise and mental stimulation (puzzle feeders, training games, scent work) can redirect that foraging energy toward safer outlets.
Keeping Parasite Prevention Current
If your dog eats earthworms with any regularity, staying on top of parasite prevention becomes especially important. Broad-spectrum dewormers that cover roundworms and hookworms form the baseline of most prevention protocols. For dogs with higher exposure risk, your vet may recommend periodic fecal exams to catch infections that standard preventatives don’t cover, like lungworm. A fecal test can identify parasite eggs before symptoms develop, making it the simplest way to catch a problem early. Dogs who eat earthworms, slugs, snails, or other invertebrates regularly should have fecal exams at least once or twice a year beyond what’s included in their standard wellness visits.