Arizona Bark Scorpion: Facts, Venom, Habitat and Range

What does an Arizona bark scorpion look like?

The bark scorpion is a slender, lightly built scorpion. Its color ranges from pale yellow to light tan or brown, and some individuals, especially in more humid places, have faint darker stripes along the back. The pincers (pedipalps) are long and thin, and the tail is slim and segmented, ending in a curved stinger.

A useful clue is a small tooth-like bump just below the stinger, called a subaculear tooth, found in many members of the genus Centruroides. You would need a close, safe look or a magnified photo to see it, but it helps experts separate bark scorpions from other species.

Bark scorpions often carry the tail coiled to one side rather than arched high over the back, the classic pose of many other scorpions. Like nearly all scorpions, they glow blue-green under ultraviolet light, which is why people sometimes spot them at night with a UV flashlight. You can read more about this in why scorpions glow under UV light.

How big are Arizona bark scorpions?

Adults usually measure about 5–8 cm (2–3 in) from the front of the head to the tip of the stinger. Males reach the upper end of that range, up to about 8 cm (3.1 in), and have a noticeably longer, thinner tail. Females are slightly shorter, up to about 7 cm (2.8 in), and have a sturdier body, especially when carrying young.

Scorpions this size are extremely light. Weights are rarely published, but an adult bark scorpion weighs around 1 g (0.04 oz) or less. Despite their small size, they are the scorpions that matter most to doctors in Arizona.

How to tell bark scorpions from other Arizona scorpions

Arizona has dozens of scorpion species, and most of them are ground-dwellers with thicker pincers. Three comparisons help:

The giant desert hairy scorpion is the largest scorpion in North America, but its venom is much weaker than the bark scorpion’s. Farther east, from New Mexico through Texas, the related striped bark scorpion (Centruroides vittatus) is the most common species, with two dark stripes on the back and a milder venom.

The name Centruroides exilicauda appears in many older books and websites. Scientists once treated the Arizona bark scorpion as part of that species, but they now separate them: C. exilicauda is the Baja California bark scorpion, while C. sculpturatus is the species of Arizona and the surrounding Sonoran Desert.

Habitat and range

The Arizona bark scorpion is native to the Sonoran Desert region. In the United States it lives across most of southern and central Arizona, with smaller populations in southeastern California, southern Nevada, the far southwest corner of Utah and western New Mexico. In Mexico it occurs mainly in the state of Sonora, with records reaching into Chihuahua.

Within this range it prefers places with a little extra moisture. It is common in riparian woodlands along washes and rivers, with mesquite, cottonwood and sycamore trees, and on rocky slopes with crevices. It also thrives in cities such as Phoenix and Tucson. Irrigated lawns, gardens, block walls and wood piles provide shelter, humidity and plenty of insects, so bark scorpions can be more numerous in some neighborhoods than in the surrounding open desert.

Climbing, hiding and winter clusters

The bark scorpion is a climber, which is unusual among scorpions of the American Southwest. Hooked claws at the tips of its legs and fine bristles let it cling to rough surfaces such as tree bark, wood, stone, stucco and brick, and it can walk across ceilings. Smooth glass, polished metal and glazed surfaces give it little to grip, which is why bark scorpions found in sinks and bathtubs often cannot climb back out.

During the hot day, bark scorpions hide under loose bark, rocks, boards and debris, in cracks in walls or in roof spaces. They are well known for resting upside down on the underside of objects, a habit scientists call negative geotaxis. This is one reason people get stung: they pick up a board, a garden pot or a shoe without seeing the scorpion clinging beneath it. Our article on whether scorpions can climb walls explains how they do it.

In cooler months bark scorpions become less active and often gather in groups in sheltered crevices. These winter clusters can contain from a few to a few dozen scorpions. Biologists think clustering helps them save moisture, although the exact reasons are still studied. Activity rises again in spring, and sightings peak during the warm months from about April to October.

What do Arizona bark scorpions eat?

Bark scorpions are nocturnal predators of small invertebrates. Their prey includes crickets, cockroaches, beetles, moths and other insects, as well as spiders and smaller scorpions, sometimes of their own species. They are mostly sit-and-wait hunters: a scorpion waits on a wall, a branch or the ground and senses prey through vibrations and fine sensory hairs on its pincers and legs.

When prey comes close, the scorpion seizes it with the pincers and, if it struggles, stings it. Like other scorpions, it digests food partly outside the body, tearing off small pieces with its mouthparts (chelicerae) and soaking them in digestive fluid. A scorpion can survive weeks or even months without food, thanks to its slow metabolism and waxy, water-saving outer skeleton.

Reproduction and life cycle

Mating begins with a courtship “dance” in which the male grasps the female’s pincers and leads her back and forth until he finds a firm surface. He deposits a sperm packet (spermatophore) on the ground and maneuvers the female over it so that she can take it up.

Bark scorpions, like all scorpions, give birth to live young. After a pregnancy of several months, a female usually produces about 25–35 young, which are pale and soft. They climb onto her back at birth and ride there until their first molt, about one to three weeks later. Once they have molted, they gradually leave and live on their own. See do scorpions carry their babies for more on scorpion family life.

Young bark scorpions molt several times, usually about five or six, before they become adults. Growth depends on temperature and food, and young scorpions generally take a year or more to reach adult size.

How long do Arizona bark scorpions live?

Arizona bark scorpions can live for about 6 years. Many die younger, eaten by predators or killed by heat, cold and drought, but those that survive the first months can live several years in sheltered places.

Predators and threats

Many animals eat bark scorpions. Predators include pallid bats, owls and other night birds, lizards, snakes, tarantulas and other large spiders, centipedes, and larger scorpions.

The best-known scorpion hunter is the southern grasshopper mouse (Onychomys torridus). A study published in Science in 2013 found that bark scorpion venom blocks pain signals in these mice instead of causing pain, because of a small change in a sodium channel in their nerves. The mice can therefore attack scorpions that would cause severe pain to other mammals.

As a widespread and adaptable species, the bark scorpion faces no major threat. Development removes some natural habitat but also creates new shelter in towns.

Venom and risk to people

The bark scorpion’s venom contains neurotoxins that act on sodium channels in nerve cells, which is why stings cause intense pain, numbness and tingling. In most adults, symptoms stay near the sting and fade within one to three days. Severe reactions, which can include muscle twitching, roving eye movements, drooling and trouble breathing, are seen mostly in young children and sometimes in older adults.

Stings are common: poison centers in Arizona receive thousands of calls about scorpions every year. Deaths, however, have been very rare since the late 1960s, thanks to better hospital care and antivenom. In 2011 the US Food and Drug Administration approved an antivenom for Centruroides scorpions, used in hospitals for the most serious cases.

Bark scorpions do not attack people. Stings happen when someone touches, steps on or traps a scorpion, for example by walking barefoot at night or putting on a shoe or glove where one is hiding. Leave scorpions alone, and if anyone has severe symptoms after a sting, especially a child, seek emergency medical help immediately or call 911. For a closer look at the risk, see is the Arizona bark scorpion deadly?, and compare it with the North African deathstalker.

Conservation status

The Arizona bark scorpion has not been assessed by the IUCN Red List, so its official status is Not Evaluated. Only a handful of the world’s 2,500-plus scorpion species have been assessed. Within its range it is common and often abundant, especially in irrigated urban areas, and there is no sign that it is declining.