Tarantulas are hairy because their hairs do far more than just cover their bodies. Every hair serves a specific purpose: sensing the environment, defending against predators, gripping surfaces, and even detecting airborne chemicals. What looks like simple fur is actually a sophisticated toolkit that tarantulas depend on for survival.
Hair as a Sensory System
Tarantulas don’t have great eyesight. Most species can barely distinguish light from dark, so they rely almost entirely on their hairs to understand the world around them. Specialized hairs called setae pick up vibrations from the ground and air, letting tarantulas detect approaching prey, potential mates, or threats without seeing them. These hairs are so sensitive they can register the faintest footsteps of an insect walking nearby.
Some of these hairs also function as chemical detectors. Spiders have two types of sensory hairs for this purpose. One type, located on the tips of their legs and pedipalps (the small appendages near their mouth), works through direct contact, essentially letting the spider “taste” surfaces it touches. The other type detects airborne chemicals and has been found exclusively on adult males in some spider species. These scent-detecting hairs sit on leg segments that rarely touch the ground, which makes sense for their job: picking up chemical signals released by females. This system helps males track down potential mates from a distance, even without being able to see them.
A Built-In Defense Weapon
One of the most unique functions of tarantula hair is self-defense, but only for species found in the Americas. These “New World” tarantulas have a special type of barbed hair on their abdomens called urticating hairs. When threatened, a tarantula will turn away from the danger, then use its hind legs in a rapid rubbing motion to kick clouds of these tiny barbed hairs into the air toward the threat. The hairs are microscopically barbed, meaning they embed themselves in skin, eyes, or mucous membranes on contact, causing intense irritation.
Not all New World species kick their hairs airborne. Some only release urticating hairs through direct physical contact, using them as a passive defense when a predator actually touches their abdomen. Either way, the result is the same: a painful, itchy deterrent that makes a predator think twice about trying again.
Tarantulas native to Africa, Asia, and the Middle East, known as “Old World” species, lack urticating hairs entirely. Instead, these species rely on more aggressive defensive behavior. When threatened, they spread their legs wide, raise their front legs to expose their fangs, and are generally much more willing to bite. The absence of urticating hairs in Old World species likely explains why they’ve evolved to be more defensively aggressive compared to their calmer New World relatives.
How Urticating Hairs Affect Humans
For tarantula owners, urticating hairs are more than a curiosity. When these tiny barbed hairs land on human skin, they cause an itchy, red, bumpy rash. The reaction is mechanical and inflammatory, not venomous, but it can be persistent and uncomfortable.
Eye exposure is where things get more serious. Hairs that land on the surface of the eye cause redness, light sensitivity, and the sensation of something stuck in the eye. If the hairs stay superficial, they cause mild irritation that can resolve quickly, sometimes within two days if the hairs are removed. But hairs that aren’t removed can slowly migrate deeper into the eye tissue over a period of two to nine weeks, potentially triggering a more significant inflammatory response inside the eye. Rubbing the eyes after exposure can make this migration worse. In most cases, inflammation can be managed with anti-inflammatory eye drops over three to four months, but in rare severe cases, deeper inflammation has persisted for more than two years. The hairs themselves can remain visible in eye tissue for up to 12 months before they break down.
Climbing With Microscopic Grip Pads
Tarantulas can climb smooth vertical surfaces, even glass, and their hairs make this possible. The undersides of their feet are covered in dense pads of specialized hairs called scopulae, along with tufts of hair beneath their claws. These hairs split into thousands of tiny tips, each ending in a flattened spatula shape. When pressed against a surface, these spatula tips generate adhesion through weak molecular forces that add up across thousands of contact points.
The system works through a clever division of labor. Scopulae on the broader foot surface generate grip when the leg pushes against the surface, which is especially useful during climbing. Claw tufts at the leg tips generate grip when the leg pulls, helping during horizontal walking. Researchers studying both tree-dwelling and burrowing species found that tarantulas use these two pad types in a complementary way, switching between them depending on the angle and direction of movement. Even rear legs contribute: scopulae on the back feet contact the surface during vertical climbing, adding extra grip where it’s needed most.
Hair Loss and the Molting Cycle
If you keep tarantulas, you’ll eventually notice bald patches on your spider’s abdomen. In New World species, this is almost always a sign that the tarantula has been kicking urticating hairs, not necessarily that a molt is approaching. This is a common misconception among new keepers.
The actual indicator of an upcoming molt is the color of the bald spot. As a tarantula prepares to shed its exoskeleton, a new exoskeleton forms underneath the current one. This makes the abdomen, especially any bald areas, appear dark and shiny, almost black. That darkening is the reliable pre-molt sign, not the bald spot itself. A tarantula can have a bald abdomen for weeks without molting, and some tarantulas enter pre-molt with a fully haired abdomen. When the tarantula does molt, it sheds the entire outer layer and emerges with a fresh coat of hairs, including a full set of new urticating hairs on the abdomen.
Why Hair Instead of Armor
Many arthropods rely on thick exoskeletons for protection, but tarantulas have invested heavily in hair instead. This makes sense given their lifestyle. A heavily armored body would be heavier and more rigid, making it harder to squeeze into burrows, climb vegetation, or move quickly when ambushing prey. Hair provides a lighter, more versatile solution: sensory coverage across the entire body, a renewable defensive weapon, adhesive grip for climbing, and the ability to detect chemical signals in the air, all without adding significant weight. Each time a tarantula molts, its full complement of hairs is restored, meaning the system is self-renewing in a way that damaged armor would not be.