The question of whether a brown tarantula is poisonous often arises from a common misunderstanding of biological terms. All tarantulas are venomous creatures, not poisonous. Their bite, while often intimidating due to the spider’s size, is generally considered to pose a low medical risk to a healthy adult human. For most New World species, which include many common brown tarantulas, the effects of a bite are frequently compared to a common bee or wasp sting.
Clarifying Venom Versus Poison
The distinction between a venomous and a poisonous organism rests entirely on the method of toxin delivery. A venomous animal, such as a tarantula, injects a toxin into another creature using a specialized apparatus like fangs or a stinger. This mechanism is an active process used for defense or to subdue prey.
A poisonous organism, in contrast, delivers its toxins passively, typically through ingestion or physical contact. Poison dart frogs, for instance, are poisonous because their toxins must be absorbed through the skin or consumed to cause harm.
Tarantulas produce venom in their chelicerae, or fangs, which is forcibly injected into a target. The venom is a complex cocktail of neurotoxins and other compounds, primarily designed to paralyze or kill smaller prey. The chemical composition of the venom is usually not potent enough to cause severe systemic effects in a large mammal like a human.
Understanding Urticating Hairs
Beyond their venom, most brown tarantulas native to the Americas, known as New World species, possess a unique and often more irritating defense mechanism: urticating hairs. These are specialized, microscopic bristles, or setae, located on the spider’s abdomen.
When threatened, the tarantula rapidly rubs its hind legs against its abdomen, effectively “flicking” a cloud of these hairs toward the perceived threat. These tiny, sharp bristles are designed to detach easily and embed themselves in the skin or mucous membranes of an attacker. The resulting reaction is primarily mechanical irritation, often presenting as an itchy, red rash.
This rash can cause intense itching, redness, and inflammation that may persist for several days or even weeks. If the hairs make contact with the eyes, they can cause a serious condition called ophthalmia nodosa, where the barbed setae become lodged in the cornea or conjunctiva. Inhaling the hairs can also lead to respiratory irritation.
Assessing the Severity of a Bite
While the urticating hairs are the most common source of human discomfort, a tarantula bite delivers venom and is a distinct defensive action. A bite only occurs when the spider feels severely threatened or is handled improperly, as their first instinct is usually to flee or deploy hairs. The fangs penetrate the skin, injecting a small amount of venom.
The immediate symptoms of a bite typically involve localized pain at the puncture site, often described as a throbbing or burning sensation similar to a wasp sting. This is usually accompanied by mild swelling and redness in the surrounding area. Minor muscle cramping or joint stiffness may occur but generally subsides within a few hours.
Tarantula venom is not considered medically significant to a healthy human, and there are no recorded human fatalities from a tarantula bite. However, there is always a risk of a severe allergic reaction, or anaphylaxis. Symptoms such as difficulty breathing, a rapid heart rate, or swelling of the face and throat necessitate immediate medical attention. First aid for a non-allergic bite involves washing the area with soap and water and applying a cold compress to reduce swelling.