Tarantulas are large, often hairy spiders that cause concern due to their size and appearance. Despite common fear, these arachnids are generally timid and only bite as a last resort when threatened or mishandled. The bite is a defensive action, and the outcome is rarely a medical emergency for a healthy human.
Defense Mechanism
Before resorting to a bite, most New World tarantulas employ a specialized defense: urticating hairs. These fine, barbed bristles, known as setae, are densely packed on the spider’s abdomen. When provoked, the tarantula rapidly rubs its hind legs against its abdomen, kicking a cloud of these microscopic hairs toward the perceived threat.
Upon contact with human skin, these minute, barbed setae embed themselves, triggering an inflammatory reaction. This usually manifests as intense itching, redness, and a localized rash that can persist for days or weeks. The hairs can cause serious issues if they enter sensitive mucous membranes, such as the eyes or respiratory tract, potentially leading to inflammation of the cornea or difficulty breathing. Old World tarantulas (found in Africa and Asia) typically lack these hairs, which may be why they are considered to possess more potent venom and a more defensive posture.
Understanding the Bite Itself
A tarantula bite is delivered through a pair of large fangs (chelicerae), resulting in two small puncture marks. The bite is almost exclusively defensive; the spider often administers a “dry bite,” injecting little to no venom to conserve resources. When venom is injected, the effects are generally mild, often compared to the sensation of a bee or wasp sting.
The venom is not considered medically significant or life-threatening to a healthy human, though it is potent enough to subdue prey. Immediate symptoms typically include localized pain, mild swelling, and redness at the puncture site. In rare instances, systemic symptoms like mild muscle cramping, fatigue, or nausea can occur, but these are usually transient.
Immediate Actions Following Contact
If bitten by a tarantula, remain calm and wash the affected area thoroughly with soap and water to prevent bacterial infection. Applying a cool compress or ice pack helps reduce localized swelling and pain. Over-the-counter pain relievers can be taken for discomfort, and the limb should be elevated if the bite occurred on an arm or leg.
For exposure to urticating hairs, the immediate goal is to remove the barbed setae from the skin. This can be done by gently applying and peeling away adhesive tape, which pulls the hairs out. The area should then be washed with water, and antihistamine creams or oral medication can help manage the intense itching and rash. Seek medical assistance immediately if the hairs entered the eyes or if you experience signs of a severe allergic reaction, such as difficulty breathing, throat swelling, or widespread rash.