Tarantulas are generally docile animals that only bite as a final defensive measure when they feel threatened or are handled roughly. A tarantula bite involves the spider injecting venom through its fangs. The venom of most species native to North America is considered mild and not medically significant to humans. Identifying a bite requires separating the physical mark left by the fangs from the body’s subsequent reaction to the venom or shed hairs.
Identifying the Puncture Wounds
The physical mark of a tarantula bite is created by the chelicerae, the paired appendages that contain the fangs. Tarantula fangs typically leave two small, close-set puncture marks on the skin, usually parallel to each other. The exact separation and visibility depend on the size and species of the spider involved.
These fang marks are often likened to two tiny pinpricks. With smaller or juvenile tarantulas, the marks may be faint or entirely invisible. Immediately after the bite, the skin at the site of penetration may show localized redness, which is a result of the mechanical trauma of the fangs piercing the skin.
Immediate Localized Symptoms
The primary visible sign of a tarantula bite is the body’s localized inflammatory response to the injected venom. Most individuals report immediate pain at the site, often described as similar to a bee or wasp sting. This throbbing pain can persist for several hours after the initial envenomation.
Accompanying the pain is the rapid onset of localized redness (erythema) and mild to moderate swelling (edema) around the wound site. The area may also feel warm due to increased blood flow. For most North American species, these localized symptoms are the extent of the reaction and typically resolve within a few hours to a couple of days.
When to Seek Medical Attention
Most tarantula bites are not medically serious and can be managed with simple first aid. Initial care involves washing the bite area thoroughly with soap and water to prevent secondary infection. Applying a cool compress or an ice pack can help reduce the localized pain and swelling.
Medical attention should be sought if localized symptoms worsen significantly or fail to improve after a few days. Immediate emergency care is necessary if signs of a systemic or allergic reaction appear. These severe reactions include difficulty breathing, widespread swelling beyond the bite site, swelling of the lips or throat, profuse sweating, nausea, vomiting, or a rapid heart rate. These symptoms indicate a severe allergic response to the venom and require immediate treatment.
Reactions Caused by Urticating Hairs
Many people who believe they have been bitten have actually only contacted the tarantula’s urticating hairs, which cause a distinct and often more irritating reaction than the venom. Urticating hairs are tiny, barbed bristles found primarily on the abdomen of New World tarantula species. The spider uses them as a primary defense mechanism, and when threatened, it may rapidly rub its hind legs across its abdomen to flick a cloud of these minute hairs toward the perceived danger.
The barbed structure allows the setae to easily embed themselves in the skin, acting like microscopic splinters. Skin exposure results in an intensely itchy, papular rash (urticaria), accompanied by redness and inflammation. The reaction is caused by both the mechanical irritation of the barbs and a chemical histamine response.
Unlike a bite, the hair reaction typically affects a wider area of skin and can persist for weeks. If hairs are suspected, adhesive materials like tape can be applied repeatedly to the affected area to pull out the embedded bristles. Topical steroid creams and oral antihistamines are used to manage the intense itching and inflammation.
The most serious consequences occur when these microscopic hairs enter sensitive mucous membranes, such as the eyes or respiratory system. Ocular exposure can cause pain, severe irritation, and lead to conditions like conjunctivitis or inflammation of the cornea, sometimes requiring specialized medical removal. Inhaling the hairs may trigger respiratory issues like rhinitis, coughing, or wheezing.