Tarantulas are among the largest spiders in the world, recognized for their hairy bodies and impressive size. All tarantula species are categorized as venomous rather than poisonous. While they possess a specialized toxin, the majority pose a low health risk to healthy humans. The overall danger level depends on the tarantula’s geographic origin and specific defense strategy.
Venom vs. Poison: Clarifying the Danger
The distinction between venom and poison lies in the mechanism of toxin delivery. Venom is actively injected (typically through a bite or sting), while poison is passively absorbed, inhaled, or ingested. Tarantulas are venomous because they use their chelicerae, or fangs, to inject a complex mixture of neurotoxic peptides and enzymes into prey or a perceived threat. This venom is designed to immobilize and begin the external digestion of small prey, such as insects and rodents.
Tarantulas use their fangs to deliver the venom, which then acts as a digestive fluid to liquefy the prey’s internal tissues. The effects of the venom on humans are generally mild because the toxin is not potent enough to cause serious systemic harm. For most species, a bite is comparable to a bee or wasp sting, causing localized pain, swelling, and redness at the injection site.
Urticating Hairs: The Non-Bite Defense
For many species, the primary defense against large predators is their urticating hairs. These are barbed, irritating bristles, or setae, covering the dorsal and posterior surface of the abdomen. When threatened, the spider rapidly deploys these hairs by rubbing its hind legs against its abdomen, effectively kicking a cloud of microscopic irritants toward the perceived danger. Some species may also passively rub the hairs onto surfaces near their burrows as a territorial warning.
Upon contact, the tiny, barbed hairs become embedded in the skin, causing intense itching, a rash, and localized inflammation that can last for days or weeks. Exposure to these hairs is particularly problematic if they are inhaled, potentially leading to respiratory irritation, or if they enter the eyes, where they can cause a condition called ophthalmia nodosa. This mechanical defense is highly effective against small mammal predators.
Assessing Risk: Old World vs. New World Species
Tarantulas are broadly categorized into two groups based on native geography, which correlates with their defensive strategy and risk profile. New World species are native to the Americas and possess urticating hairs as a first line of defense. These species are typically more docile, less likely to bite, and generally have venom with low medical significance to humans, resulting in only mild, localized pain.
Old World species, found in Africa, Asia, and Europe, do not possess urticating hairs and rely on a different defense mechanism. These tarantulas are faster, more defensive, and possess potent venom. A bite from an Old World species can cause severe pain, muscle cramping, and systemic effects, though fatalities are rare. For example, species in genera like Poecilotheria and Haplopelma are known to cause symptoms such as intense muscle spasms and exhaustion.
Immediate Symptoms and Treatment
A tarantula bite, especially from a New World species, typically presents with symptoms similar to a mild insect sting. Localized pain, redness, and swelling at the site of the fang marks are the most common initial reactions. For minor envenomations, basic first aid involves washing the area with soap and water to prevent infection and applying a cold compress to reduce swelling and pain.
Contact with urticating hairs results in an intensely itchy rash, which may be treated with topical corticosteroid creams or oral antihistamines to manage the allergic reaction. To remove embedded hairs from the skin, a technique involving the application and removal of sticky tape can be used effectively. If a person experiences severe symptoms, such as chest tightness, difficulty breathing, or symptoms of a known Old World bite, immediate medical attention is necessary for supportive care, including pain management and monitoring for systemic effects.