Tarantulas are among the largest and hairiest spiders, leading to questions about their potential danger to humans. All tarantulas are venomous and possess the ability to inject toxins through their fangs. However, their venom is not considered a threat to human life; a bite from most species results in symptoms comparable to a common bee or wasp sting. Most tarantula-related injuries involve a different defense mechanism that does not use venom.
Understanding Tarantula Venom
Tarantula venom is a complex biological tool primarily evolved for subduing prey, not defending against large predators. This venom is a cocktail containing neurotoxins, which attack the nervous system, and various enzymes that break down the prey’s tissues. The spider injects this mixture into insects, small rodents, or other small vertebrates using its chelicerae (fangs). The neurotoxins cause rapid paralysis, allowing the spider to safely consume its meal. While the venom’s chemical composition varies widely across the more than 1,000 species, its compounds do not have a medically significant effect on human physiology.
Human Reaction and Risk Assessment
A tarantula bite typically causes only localized symptoms in humans, often likened to a bee sting. Common reactions include immediate, sharp pain at the bite site, followed by mild redness, swelling, and a temporary increase in skin temperature. These effects are transient and usually resolve within a few hours or a couple of days.
The severity of a bite depends on the species, which are categorized as New World (the Americas) or Old World (Africa, Asia, Europe). Old World tarantulas lack an alternative defense mechanism, resulting in venom that is generally more potent or “medically significant.” Bites from these species can cause more intense symptoms, including muscle cramping, nausea, and persistent joint stiffness, though they are rarely life-threatening.
Systemic allergic reactions, such as anaphylaxis, are rare but possible, as with any insect or spider bite. Medical attention is advised if a bite results in severe, widespread swelling, breathing difficulty, or signs of a generalized allergic response. Otherwise, treatment involves cleaning the wound, elevating the affected limb, and managing pain with over-the-counter analgesics.
The Role of Urticating Hairs
Many tarantulas, particularly New World species, rely on a secondary, non-venomous defense mechanism: urticating hairs. These tiny, barbed bristles are densely packed on the tarantula’s abdomen and serve as its preferred defense. When threatened, the spider rubs its hind legs against its abdomen, “kicking” a cloud of irritating hairs toward the attacker. The barbed hairs easily embed in the skin, eyes, and mucous membranes.
Human contact with urticating hairs results in urticaria, presenting as a rash, severe itching, and inflammation that can last for hours or weeks. This irritation is often a more common interaction with pet tarantulas than an actual bite. Contact with the eyes is concerning, as the hairs can embed in the cornea and conjunctiva, potentially leading to serious complications like ophthalmia nodosa. If inhaled, the hairs can also irritate the respiratory tract, causing coughing and breathing discomfort.