The bark scorpion, Centruroides sculpturatus, is the single most venomous scorpion species found in North America, posing a significant health risk across the Southwestern United States and Northern Mexico. It is a member of the Buthidae family, which includes many of the world’s medically relevant scorpions. The neurotoxic nature of its venom sets it apart from most others found on the continent. This small arachnid has adapted to both arid desert environments and heavily populated urban areas, where it frequently infests human dwellings.
Identifying Characteristics
The bark scorpion is relatively small, with mature adults typically reaching a body length of between 2 and 3 inches. Its coloration is generally a pale yellow or light tan, allowing it to camouflage effectively against the sand, rocks, and tree bark. A distinguishing feature is its slender build, including an elongated, thin tail (metasoma) and delicate pincers. These traits contrast with the robust tails and thick pincers of many other common scorpion species.
Unlike scorpions that hold their tail arched over their back, the bark scorpion often rests with its tail coiled down to the side, parallel to the surface. This slender profile and side-coiling habit help distinguish it from less medically significant species. Like many scorpions, it fluoresces a bright greenish-blue color under ultraviolet (UV) light, which aids in nighttime detection.
Geographic Range and Environment
The primary distribution of Centruroides sculpturatus is concentrated in the Sonoran Desert region of the Southwestern US and Northern Mexico. In the US, its range extends across most of Arizona, western New Mexico, southern Nevada, southern Utah, and southeastern California. This arachnid thrives in arid and semi-arid landscapes, where it naturally seeks refuge under rocks, wood piles, and loose tree bark, which is the source of its common name.
The bark scorpion is highly adaptable, and its presence has increased in urban areas due to irrigated lawns and landscaping, which create pockets of moisture and humidity. It is a skilled climber, allowing it to scale walls, trees, and the stucco of houses. They are frequently found inside homes, seeking shelter in dark, moist spaces like wall voids, closets, sinks, and bathtubs.
Toxicity and Medical Implications
The venom of the bark scorpion contains a potent mixture of neurotoxins that directly affect the nervous system. Immediately following a sting, the patient experiences intense, sharp, burning pain at the site, often followed by numbness and a tingling sensation (paresthesia) that can spread outward from the wound. The neurotoxic action can lead to more severe, systemic symptoms, particularly in vulnerable populations.
Severe envenomation is more common in young children, who lack the body mass to dilute the toxin, and in the elderly or those with underlying health conditions. Systemic effects include neuromuscular dysfunctions, such as involuntary muscle jerking, twitching, and uncontrolled shaking of the extremities. Cranial nerve dysfunction may also manifest as slurred speech, hypersalivation, and abnormal eye movements. The most concerning complication is respiratory distress, which can necessitate mechanical ventilation due to the loss of muscle control in the pharynx and diaphragm.
While stings are common, fatalities are rare due to advancements in medical care and the availability of a specific treatment. For severe cases, particularly in children, a specialized antivenom called Anascorp is available. This antivenom works by binding to the venom’s toxins, rapidly reversing the systemic neurotoxic effects.
Activity and Life Cycle
The bark scorpion is primarily a nocturnal hunter, typically emerging after sunset to forage for prey. Its diet consists mainly of small arthropods, which it ambushes or actively seeks out, including:
- Spiders
- Crickets
- Beetles
- Other insects
The life cycle begins with live birth, a reproductive method that sets them apart from many other arachnids. A female gives birth to between 25 and 35 live young, which immediately climb onto her back for protection. The juvenile scorpions remain riding on their mother for up to three weeks until they undergo their first molt. Bark scorpions often congregate in groups of up to 30 individuals to overwinter in sheltered locations.