If you’ve spotted a dark, worm-like creature in your Florida yard, you’re most likely looking at one of three things: a New Guinea flatworm, a black velvet slug, or a hammerhead flatworm. All three are invasive species, all are active in warm, moist conditions, and each looks different enough to tell apart once you know what to check for.
New Guinea Flatworm
The New Guinea flatworm is the species Florida residents encounter most often when they describe finding a “black worm.” It’s a flat, smooth, olive-black creature about two to three inches long with a pale stripe running down its underside. Unlike an earthworm, it has no segments and glides along surfaces rather than burrowing through soil. You’ll typically find it at night or after rain, hiding under rocks, pavers, mulch, flower pots, or leaf litter during the day.
This flatworm is a serious problem for Florida’s ecosystem because it feeds on native snails and earthworms, reducing populations that are important for soil health and as food for native wildlife. It reproduces quickly and spreads easily through potted plants and landscaping materials. The Florida Fish and Wildlife Conservation Commission considers it an invasive species and recommends killing them when found.
Black Velvet Slug
The black velvet slug (sometimes called the leatherleaf slug) is another dark creature commonly mistaken for a worm. Native to South America, it’s now established across northern and central Florida and the rest of the Gulf Coast. Adults are uniformly black on top with a velvety texture and a paler underside. Juveniles are lighter and sometimes have a pale stripe down the middle. At full size, they reach about two inches long and weigh only around a gram.
You’ll find black velvet slugs in lawns, drainage ditches, under potted plants in nurseries, and in other damp, disturbed areas near homes. They burrow into soft soil and can enter the root balls of container plants through drainage holes, which is how they hitch rides to new locations. They eat both living and decaying leaves. Despite their alien appearance, they aren’t considered a significant garden pest in Florida because they rarely reach high numbers in any one area.
Hammerhead Flatworm
If the black worm you found has a distinctly fan-shaped or arrow-shaped head, it’s a hammerhead flatworm. These can grow considerably longer than New Guinea flatworms, sometimes reaching a foot or more. They’re typically dark brown to black with one or more pale stripes. Like the New Guinea flatworm, hammerheads prey on earthworms and are considered invasive in Florida.
One important note: never cut a hammerhead flatworm in half. These flatworms can regenerate from fragments, so slicing one up can create multiple worms. Salt or citrus oil applied directly to the worm are effective ways to kill them.
Health Risks to Know About
Both flatworms and slugs in Florida can carry rat lungworm, a parasitic roundworm that normally cycles between rats and snails or slugs. The parasite’s larvae live inside infected slugs and snails. If a person accidentally swallows a slug, a snail, or even slime residue left on unwashed produce, the larvae can travel to the brain and cause a form of meningitis. Most infections produce mild or no symptoms, but serious cases involve severe headache, neck stiffness, nausea, tingling sensations, vision changes, and confusion. Rare complications include hearing loss, memory problems, and seizures.
The practical takeaway: don’t handle any of these creatures with bare hands. New Guinea flatworms secrete stomach fluids that can irritate skin, and any slug or flatworm could potentially carry parasites. If you do touch one accidentally, wash your hands thoroughly. Always wear gloves when removing them from your garden, and wash homegrown produce carefully, especially leafy greens that slugs may have crawled across.
How to Remove Them From Your Yard
For New Guinea flatworms, the most effective home method is hot water. Soaking infested soil with water between 109 and 120 degrees Fahrenheit for five minutes kills the flatworms without damaging plant roots. You can also pour boiling water directly onto individual worms to kill them quickly. This works well for flatworms found under pots, pavers, or garden debris.
For hammerhead flatworms, skip the knife and use salt or citrus oil instead. Place the worm in a container with salt, or apply the salt directly. Citrus-based solutions also break down their soft bodies effectively.
For black velvet slugs, standard slug control methods work: beer traps, iron-based slug bait, or simply collecting them by hand (with gloves) at night when they’re active. Because their populations in Florida tend to stay low, you may not need aggressive control unless you’re seeing them regularly on garden plants.
Regardless of species, reducing moisture and hiding spots around your home goes a long way. Clear leaf litter, elevate pots off the ground, and minimize mulch depth near foundations. These creatures all depend on damp, sheltered environments, and making your yard less hospitable is the most lasting solution.