The Missouri tarantula (Aphonopelma hentzi) is the largest spider species found in the state, often encountered in the southern half of Missouri. To answer the most pressing question directly: the Missouri tarantula is venomous, but its venom is not considered a serious threat to human health. While they possess venom to subdue their prey, their defensive behaviors are generally mild toward people.
Are They Venomous or Poisonous?
The distinction between venomous and poisonous is based on the method of toxin delivery. An organism is defined as poisonous if its toxins are harmful when absorbed, inhaled, or ingested (e.g., certain mushrooms). Conversely, an organism is considered venomous if it actively injects its toxins, typically through a bite or a sting (e.g., snakes, wasps). The Missouri tarantula is venomous because it uses fangs to inject a mild neurotoxic and cytotoxic venom into its prey or, rarely, in defense.
The venom of Aphonopelma hentzi is primarily effective against the small arthropods and insects that make up its diet. Although the venom contains components that can affect the nervous system or break down tissue, the quantity and potency are medically insignificant for a healthy human. A bite is often compared to a mild bee or wasp sting in terms of immediate effect and localized pain. The low toxicity ensures that minor discomfort and localized reaction are the only symptoms that occur for most people.
Identifying the Local Species
The sole tarantula species native to Missouri is Aphonopelma hentzi, also known as the Texas Brown or Oklahoma Brown tarantula. This stocky, terrestrial spider is noticeable, as females can have a leg span exceeding four inches. Their body and legs are typically dark chocolate brown, sometimes with reddish or bronze hairs covering the carapace and abdomen.
These tarantulas are mainly found in the south and central parts of Missouri; the Missouri River often acts as a northern boundary to their range. They prefer dry, rocky glades, scrublands, and grasslands, constructing silk-lined burrows or utilizing abandoned rodent tunnels for shelter. While they are nocturnal hunters, adult males become highly visible during the late summer and early fall as they search for mates.
Understanding the Bite and Other Defenses
Despite their intimidating appearance, Aphonopelma hentzi is a docile species that prefers to retreat into its burrow rather than confront a threat. A bite is uncommon, generally occurring only when the spider feels severely provoked or is accidentally pressed against the skin. If a bite occurs, the fangs cause a puncture wound that is painful due to the physical penetration.
The symptoms of a bite are generally limited to localized pain, mild swelling, and redness at the site, which resolves quickly. Systemic reactions (such as fever, nausea, or muscle cramps) are extremely rare, and the venom is not considered medically significant for humans. However, as with any arthropod bite, there is a risk of an allergic reaction requiring immediate medical attention.
The primary defense mechanism of this tarantula is not its bite, but a behavior known as “kicking” urticating hairs from its abdomen. These tiny, barbed bristles are flicked toward a perceived threat and can embed themselves in the skin or mucous membranes. Contact often causes an immediate reaction, including intense itching, an allergic rash, and inflammation that can last for several hours to weeks.
If a bite occurs, the first step is to clean the wound thoroughly with soap and water to prevent secondary infection. Applying a cool compress or ice pack for about 15 minutes per hour will help reduce localized pain and swelling. Over-the-counter pain relievers can manage discomfort, and an antihistamine or calamine lotion may alleviate itching.
If you encounter urticating hairs, the initial goal is removal. Apply adhesive tape (like duct tape) to the affected area to pull them out. Afterward, rinse the area with cold water and apply a cool compress to soothe the irritation. Over-the-counter antihistamine creams or oral antihistamine pills can help manage the resulting allergic reaction, which is a localized hive response. Seek professional medical help immediately if you experience signs of a severe allergic reaction, such as difficulty breathing, swelling of the face or throat, or widespread rash.