The Arizona Bark Scorpion (Centruroides sculpturatus, now categorized within Centruroides exilicauda) is a small scorpion species in family Buthidae endemic to the Sonoran Desert of the southwestern United States and northwestern Mexico. It is primarily found in Arizona, USA, and Sonora, Mexico, but its range extends into the borderlands of adjacent states, including western New Mexico, southern Utah, southern Nevada (including Las Vegas), and the Colorado river habitat of eastern California1. The species is noted for being the most venomous scorpion in North America4. Due to its abundance throughout its range, it is considered a pest and is not listed as a threatened species.
Bark scorpions are light yellowish brown to brown in color. Pedipalps are elongated and thin, in contrast to thicker, shorter pincers of other scorpion species. Four pairs of jointed legs and chelicerae are present. The bark scorpion has multiple eyes, with two eyes located on the top of and from 2-5 eyes located laterally on its cephalothorax7. Despite its numerous eyes, the bark scorpion’s vision is limited, and pectines (comb-like sensory organs) located on the abdomen and fine sensory hairs on the legs assist the bark scorpion with navigation, detecting prey, and finding females for mating. Adult males of the species grow up to 8 cm in length (3.14 inches), while adult females may reach up to 7 cm (2.75 inches) 1.
Centruroides exilicauda has a distinctive venomous stinger, known as a telson, located at the end of its tail. The stinger is used for defense against predation and to paralyze prey. Known predators include birds, snakes, spiders, rodents, lizards, and other vertebrates; cannibalism by other scorpions is also common4. Domestic animals, such as cats and dogs, are known to eat the bark scorpions. The bark scorpion has a diet consisting of small insects, such as roaches, beetles, and crickets, and prefers to lie in wait and ambush prey. Although the tail contains venom that is potentially lethal to human beings, the bark scorpion is not aggressive and typically does not sting humans unless provoked, or more commonly, stepped on. Fatalities, though rare, usually occur in small pets, young children, the elderly, and immuno-suppressed or allergic individuals. The average healthy human adult typically experiences symptoms for 24-72 hours that include severe pain, coupled with nausea, vomiting, and numbness; temporary dysfunction such as convulsions or immobilization localized at the sting location may also occur2. Extreme reactions to scorpion stings are characterized by numbness, paralysis, frothing at the mouth, and shortness of breath; if an extreme reaction is observed, emergency medical care should be immediately sought due to the risk of anaphylactic shock3. An anti-venom for human usage was approved by the FDA as of August 3, 2011, and can be successful at reducing symptom severity and duration of hospitalization8. Notably, the Arizona bark scorpion is born with a finite amount of venom that is not replenished over its lifespan; therefore, stings by a juvenile are more potent and potentially more dangerous than that of an adult.
Bark scorpions are well-adapted to their desert habitat due to the layers of wax on their exoskeleton which prevent water loss. Although heat tolerant, they prefer to hide under rocks, wood piles, block fences, and tree bark during the daytime desert heat, emerging at sunset to hunt prey6. They are the only known scorpion species in the southwestern United States known to be able to climb rough surfaces, and as a result can often be found climbing walls, trees, and houses5. Bark scorpions are unable to climb smooth surfaces, such as glass. Preferred habitat includes any high-humidity area with a water source that attracts prey; the prevalence of cultivated lawns and backyard swimming pools within the bark scorpion’s range makes the micro-climates of urban desert backyards ideal scorpion habitat, and therefore bark scorpions are often found inside adjacent houses3. The likelihood of finding scorpions inside a home increases during the desert fall and winter, when outdoor prey abundance and temperatures decrease. While scorpions are solitary animals during the high heat of the Sonoran Desert summer, the colder seasonal temperatures found in the area from October to March will cause the bark scorpion to congregate in nests of 20-30 animals as they hibernate for the season; this concentrated presence around a likely heat and prey source may also increase the rate of scorpion sightings within human residences during those months.
Barks scorpions are known to live up to six years. They are a viviparous species, with the female scorpion giving birth to 25-30 scorplings at a time4. Once born, the juvenile scorpions are guided onto the mother’s back, where she protects and nurtures them until the first molting of their exoskeleton, which occurs at approximately three weeks of age. The female typically does not exhibit predatory behavior towards her young during this phase, however, if prey is scarce, infanticide by the mother may occur7.
Bark scorpions, like all scorpion species, glow brightly under ultraviolet light and moonlight. This is due to a substance located within the hyaline layer of the exoskeleton. It is unknown precisely why this capability developed, although it is thought that the florescence assists in detecting lunar cycle changes; scorpions are known to be less active during moonlit nights and full moon phases9.
The Arizona bark scorpion (Centruroides sculpturatus, once included in Centruroides exilicauda) is a small light brown scorpion common to the Sonoran Desert in the southwestern United States and northwestern Mexico. An adult male can reach 8 cm in length (3.14 inches), while a female is slightly smaller, with a maximum length of 7 cm (2.75 inches).[1]
Arizona bark scorpions are eaten by a wide variety of animals such as pallid bats,[2] birds (especially owls), reptiles, and other vertebrates. Some examples include spiders, snakes, peccaries, rodents, and other scorpions. Development, pesticides and collecting scorpions for research or the pet trade also reduces the bark scorpion population.
The painful and potentially deadly venom of Arizona bark scorpions has little effect on grasshopper mice. Scientists have found the scorpion toxin acts as an analgesic rather than a pain stimulant in grasshopper mice.[3]
Arizona bark scorpions have a gestation period of several months, are born live, and are gently guided onto their mother's back. The female usually gives birth to anywhere from 25 to 35 young. These remain with their mother until their first molt, which can be up to 3 weeks after birth. Arizona bark scorpions have a life expectancy of about 6 years.[4]
Arizona bark scorpions, like most other scorpions, are incredibly resilient. During US nuclear testing, scorpions, along with cockroaches and lizards, were found near ground zero with no recorded adverse effects.[5]
The Arizona bark scorpion is nocturnal,[4] and particularly well adapted to the desert: layers of wax on its exoskeleton make it resistant to water loss. Nevertheless, Arizona bark scorpions hide during the heat of the day, typically under rocks, wood piles, or tree bark. Arizona bark scorpions do not burrow, and are commonly found in homes, requiring only 1/16 of an inch for entry.[6]
Arizona bark scorpions prefer riparian areas with mesquite, cottonwood, and sycamore groves, all of which have sufficient moisture and humidity to support insects and other prey species. The popularity of irrigated lawns, and other systems which increase environmental humidity in residential areas, has led to a massive increase in the number of these animals in some areas.
Centruroides scorpions are unusual in that they are the only genus in the Southwest that can climb walls, trees, and other objects with a sufficiently rough surface. Arizona bark scorpions practice negative geotaxis, preferring an upside down orientation, which often results in people being stung due to the scorpion being on the underside of an object.[7]
The Arizona bark scorpion preys on small and medium-sized animals such as beetles, spiders, crickets, cockroaches, other insects and other scorpions.[4][8]
The range of the Arizona bark scorpion is from southern California, southern Arizona and western New Mexico. They are also found in Baja California, Sonora and Chihuahua, Mexico.[8]
The Arizona bark scorpion is the most venomous scorpion in North America, and its venom can cause severe pain (coupled with numbness, tingling, and vomiting) in adult humans, typically lasting between 24 and 72 hours.[4] Temporary dysfunction in the area stung is common; e.g. a hand or possibly arm can be immobilized or experience convulsions. It also may cause loss of breath for a short time. Due to the extreme pain induced, many victims describe sensations of electrical jolts after envenomation. Two recorded fatalities have occurred in the state of Arizona since 1968; the number of victims stung each year in Arizona and New Mexico is estimated to be in the thousands. In Mexico, more than 100,000 people are stung annually, and during a peak period in the 1980s, the Arizona bark scorpion claimed up to 800 lives there.[9]
An antivenom was developed for this species at Arizona State University by Dr. Herbert L. Stahnke, and produced in quantities sufficient to treat individuals within the state of Arizona. This antivenom was not FDA approved, but use within the state of Arizona was allowable and very successful in shortening the duration of symptoms and hospitalization. Production of this antivenom ceased by 2000 and the product was unavailable by 2004. A Mexican-produced antivenom, Anascorp [Antivenin Centruroides (scorpion) F(ab′)2, Laboratorios Silanes, Instituto Bioclon SA de CV], received FDA approval on August 3, 2011, and is now in use.[10]
Basic first aid measures can be used to help remediate Arizona bark scorpion stings:[11]
Arizona poison control centers suggest immediate medical attention if severe symptoms occur, particularly in young children.[5] The Poison Center may be reached at 1-800-222-1222.
Arizona bark scorpions, like most other scorpions, will glow when exposed to a blacklight. This is particularly useful in scorpion detection, since Arizona bark scorpions are active during the night, and can be easily spotted using this method. Typical UV LED flashlights enable their human operator to readily detect Arizona bark scorpions at a distance of approximately six feet. Newly molted Arizona bark scorpions will not glow under ultraviolet light for a few days after molting.
Arizona bark scorpions are tan or light beige tone in color and very small, making them difficult to detect especially on natural terrain (rocky land, multiple vegetation and soil textured land). They are not known to seek out people, but look for places to hide unless provoked or defending their young. Several methods of control have historically been used to control Arizona bark scorpions, such as physical barriers (scorpions are unable to climb smooth surfaces),[12][13] pesticides,[14] glue boards, and removing any scorpion congregation areas in the vicinity of the building.
The Arizona bark scorpion (Centruroides sculpturatus, once included in Centruroides exilicauda) is a small light brown scorpion common to the Sonoran Desert in the southwestern United States and northwestern Mexico. An adult male can reach 8 cm in length (3.14 inches), while a female is slightly smaller, with a maximum length of 7 cm (2.75 inches).
