Several types of worms can cause real harm, whether they’re parasites living inside your body or invasive species destroying soil ecosystems. The most common parasitic worm infection globally, roundworm (ascariasis), affects roughly 1 billion people worldwide. Meanwhile, invasive jumping worms are reshaping forests and gardens across North America. Here’s what you need to know about the worms that cause the most damage and how to protect yourself.
Parasitic Worms That Infect Humans
Parasitic worms, called helminths, come in several major types. Each enters the body differently, causes different symptoms, and requires different treatment. Some infections produce no symptoms at all, which means you can carry worms without knowing it. Others cause serious complications including malnutrition, anemia, and organ damage.
The main categories are roundworms, tapeworms, hookworms, pinworms, whipworms, and flukes. Most spread through contaminated soil, water, or undercooked meat. In areas with poor sanitation, eggs shed in human feces contaminate the ground and take about three weeks to become infectious in the soil. From there, they can end up on unwashed vegetables, in drinking water, or on the hands of children playing in dirt.
Pinworms: The Most Common in the U.S.
Pinworms are thin, thread-like worms that spread when you touch a contaminated surface and then put your hands near your mouth. The eggs hatch in your small intestine, and at night, female worms crawl to the skin around your anus to lay eggs. This causes intense itching, especially while sleeping, which is the hallmark symptom.
If you suspect pinworms in your child, check two to three hours after they fall asleep. You can also do a tape test at home: first thing in the morning, before bathing or using the toilet, press a strip of clear cellophane tape against the skin around the anus. Eggs stick to the tape and can be identified under a microscope. For the most reliable results, repeat the test three mornings in a row. Treatment is straightforward and highly effective, with cure rates between 90% and 100% with a single dose of standard deworming medication.
Hookworms: They Enter Through Your Feet
Hookworms have one of the more unsettling transmission routes. Their larvae hatch in contaminated soil and can actively burrow through the skin of your feet if you walk barefoot. From there, they travel through your bloodstream to your heart, then your lungs. You cough them up, swallow them, and they settle into the walls of your small intestine, where they feed on blood.
A mild hookworm infection might not cause noticeable symptoms. A heavy, untreated infection drains enough blood to cause iron-deficiency anemia and protein loss. Signs include fatigue, weakness, pale skin, and abdominal pain. This is one of the reasons hookworm disease has historically been a major public health problem in tropical and subtropical regions with limited access to shoes and sanitation.
Tapeworms: From Undercooked Meat
Tapeworms spread when you eat raw or undercooked pork, beef, or fish containing larvae. Once inside your intestine, they can grow for weeks before producing symptoms, typically about eight weeks after infection. When symptoms do appear, they tend to be mild: abdominal pain, nausea, diarrhea, or constipation.
Left untreated, a tapeworm from pork can persist for two to three years. A more serious concern with the pork tapeworm specifically is that its eggs, if ingested, can form cysts in organs including the brain, a condition that causes seizures and other neurological problems. Tapeworm infections are treatable with a single dose of anti-parasitic medication, and cure rates range from about 75% to 100% depending on the species and treatment approach.
Worms You Can Catch From Pets
Dogs and cats carry roundworms and hookworms that can infect humans, particularly children who play in contaminated soil. The pet roundworm Toxocara is especially concerning. If you accidentally swallow its eggs (from dirty hands, for example), the larvae can migrate through your body and settle in your liver, lungs, or even your eyes.
When larvae reach internal organs, the condition is called visceral larva migrans. It can cause fever, fatigue, coughing, wheezing, and abdominal pain. When larvae reach the eye, it can cause visual disturbances, eye pain, and abnormal eye movements. Pet hookworms, meanwhile, can burrow into exposed skin and tunnel beneath it, leaving raised, red, itchy lines that trace the worm’s path. This is called cutaneous larva migrans, and it typically happens from walking barefoot or sitting on soil contaminated with pet feces.
Regular deworming of pets and picking up after them significantly reduces these risks.
How Parasitic Worm Infections Are Treated
Most intestinal worm infections respond well to oral deworming medications. These drugs work by disrupting the worm’s ability to absorb nutrients, essentially starving it. For roundworms and pinworms, a single dose often does the job, with cure rates above 90%. Hookworms and whipworms can be harder to clear. A single dose cures hookworm in roughly 72% to 96% of cases, but whipworm cure rates with one dose can be as low as 27%, often requiring a multi-day course.
Treatment is generally quick and well-tolerated. For most infections, you take one to three days of medication and that’s it. Tapeworms similarly respond to a single-dose treatment. The key is getting a proper diagnosis first, since different worms may need different medications or dosing schedules.
Ringworm Is Not Actually a Worm
Despite the name, ringworm has nothing to do with worms. It’s a fungal skin infection that produces a ring-shaped, red, itchy rash. The name comes entirely from its appearance. It’s treated with antifungal creams or pills, not deworming medication. If an over-the-counter antifungal product hasn’t improved the rash within two weeks, a prescription-strength treatment is typically needed.
Invasive Jumping Worms in Soil and Gardens
Not all “bad worms” live inside people. Asian jumping worms are an invasive species tearing through forests and gardens across much of the United States. Originally from East Asia, these worms (sometimes called crazy worms, snake worms, or Alabama jumpers) devour the leaf litter layer on forest floors at an alarming rate. That leaf litter isn’t just dead leaves. It’s a habitat for countless small animals and a critical layer that many plants need to grow and spread.
Jumping worms strip it away, leaving behind bare, granular soil that resembles coffee grounds. They displace native earthworms, centipedes, salamanders, and ground-nesting birds. They alter soil chemistry and the microbial communities that healthy ecosystems depend on. A population of jumping worms can invade more than five hectares (about 12 acres) in a single year. As one USDA researcher put it, “Soil is the foundation of life, and Asian jumping worms change it.”
There is currently no effective way to eliminate jumping worms once they’ve established in an area. Prevention focuses on avoiding the spread of their cocoons in soil, mulch, and compost. If you’re buying soil or plants, check for the telltale signs: worms that thrash wildly when handled and soil with an unusually grainy, coffee-ground texture.
How to Reduce Your Risk of Parasitic Worms
Most parasitic worm infections are preventable with basic hygiene and food safety. Wash your hands thoroughly after using the bathroom, after handling soil, and before eating. Cook meat to safe internal temperatures, particularly pork, beef, and freshwater fish. Wash fruits and vegetables well, especially if they were grown in regions where soil contamination is common.
Wear shoes outdoors in areas where hookworm is present, which includes many tropical and subtropical regions. Keep children’s fingernails trimmed short to reduce egg transmission from pinworms. Deworm your pets regularly and clean up their waste promptly, especially in yards and sandboxes where children play.