Adult hookworms are small, pale, thread-like worms roughly the size of a staple. Depending on the species and sex, they range from about 5 to 15 millimeters long. You’re unlikely to see one with the naked eye in a stool sample, but if you did, it would look like a tiny, slightly curved whitish or pinkish thread with a distinctive hook-shaped bend at the head end, which is how the worm got its name.
Size and Shape of Adult Hookworms
Two species cause most human infections, and they differ slightly in size. The larger species, Ancylostoma duodenale, produces males that measure 8 to 12 mm and females that measure 10 to 15 mm. The smaller species, Necator americanus, produces males of 5 to 9 mm and females of 9 to 11 mm. For reference, even the largest hookworms are shorter than a U.S. penny is wide.
Both species are cylindrical and tapered at each end, with a slightly thicker midsection. Fresh specimens appear grayish-white to pinkish, sometimes with a reddish tint from the blood they feed on. Their bodies are semi-translucent, so under magnification you can sometimes see the dark line of the gut running through the center. Females are consistently longer than males in both species. Males have a distinctive fan-shaped structure at their tail end that scientists use to tell the species apart.
The Head End: Teeth and Cutting Plates
The most striking feature of a hookworm is its mouth. Both species have a large, open mouth capsule at the head that they use to latch onto the intestinal wall and feed on blood. What’s inside that capsule differs by species. Ancylostoma duodenale has two pairs of sharp, curved teeth. Necator americanus has flat, blade-like cutting plates instead. You would only see these structures under a microscope, but they’re the key reason hookworms cause blood loss: the mouth grips the intestinal lining, and the worm secretes substances that keep blood flowing while it feeds.
What Hookworm Larvae Look Like
Before hookworms reach their adult form, they go through larval stages in soil. The infective larvae are invisible to the naked eye, measuring only 500 to 600 micrometers long (roughly half a millimeter). Under a microscope, they appear as slender, transparent worms with a pointed tail and a thin outer sheath with visible striations. These are the stage that penetrates human skin, typically through bare feet walking on contaminated soil.
What Hookworm Eggs Look Like
Hookworm is usually diagnosed not by finding worms but by finding eggs in a stool sample examined under a microscope. The eggs are oval, thin-shelled, and colorless. Inside a fresh egg, you can typically see a cluster of developing cells (usually 4 to 8) separated by a clear space from the eggshell. The eggs of both major species look nearly identical under the microscope, which is why lab technicians report them simply as “hookworm eggs” rather than trying to distinguish the species.
What Hookworm Infection Looks Like on Skin
Many people searching “what does hookworm look like” are really asking about the visible signs on the body. The most recognizable sign is a skin reaction that occurs in two stages.
The first stage happens right where the larvae enter the skin, usually on the feet, legs, or buttocks. This produces an itchy, red rash sometimes called “ground itch,” with small raised bumps at the entry point. It can look similar to a bug bite cluster or mild allergic reaction.
The second, more distinctive stage is called cutaneous larva migrans, or “creeping eruption.” This happens when hookworm larvae (often from animal species) migrate under the skin rather than penetrating deeper into the body. The hallmark is a raised, reddish, winding track about 3 mm wide that traces the larva’s path beneath the surface. The track advances a few millimeters per day, creating a snaking, irregular line that’s intensely itchy. You might see a single track or multiple tracks depending on how many larvae entered the skin. The tracks appear on whatever body part had direct contact with contaminated soil or sand. In more severe cases, fluid-filled blisters or swelling can develop along the track.
What You Won’t See
Unlike some intestinal parasites, adult hookworms rarely show up visibly in stool. They’re small, they attach firmly to the intestinal wall, and they don’t typically pass out of the body on their own during an active infection. If you’re experiencing symptoms like unexplained fatigue, iron deficiency, or a persistent itchy rash on your feet, a stool test under a microscope is the standard way to confirm the diagnosis. The worms themselves will almost certainly stay out of sight.