Arizona Bark Scorpion

For a healthy adult it is usually a very painful but survivable event, with intense burning pain at the site, a strange electric numbness that can spread up the limb, and sometimes a hypersensitivity where light touch feels like a shock. The serious cases involve the venom's effects on the nervous system, causing uncontrolled muscle movements, difficulty controlling the eyes and swallowing, agitation, and breathing problems, and these are most likely in small children, in whom a sting can be life-threatening, and in the elderly or people with heart or lung conditions. Anyone stung who develops anything beyond local pain, and any child stung, should be seen urgently; antivenom and supportive care resolve almost all cases.

Two reasons — they climb, and they seek what a house provides. Most scorpions cannot climb smooth vertical surfaces, but the bark scorpion's flattened body and clinging feet let it go up stucco walls, block, wood, and screens and cross ceilings upside down, so it can enter through roof vents, weep holes, and gaps around pipes rather than only at ground level. Once inside it looks for the same things it wants outdoors, cool dark cracks, moisture, and insect prey, which leads it to bathrooms, kitchens, closets, shoes left on the floor, and folded laundry. In bark scorpion country the standard advice is to shake out shoes and clothing, keep beds away from walls, and use a blacklight to check at night.

All scorpions fluoresce a vivid blue-green under ultraviolet light because their exoskeleton contains fluorescent chemicals, including one called beta-carboline, concentrated in a thin outer layer of the cuticle that forms as the scorpion hardens after each moult; a freshly moulted scorpion does not glow until this layer sets. The purpose is not settled. Ideas include that the whole body acts as a light sensor helping the scorpion judge when and where it is dark enough to come out safely, that the glow confuses or lures prey, or that it is simply a side effect of the cuticle's chemistry with no function. What is certain is that it makes the animals easy to find, and blacklight scorpion hunting is both a pest-control tool and a hobby in the Southwest.

Arizona has dozens of scorpion species, and the others are far less of a concern. The giant desert hairy scorpion is the largest in North America but has weak venom and a sting like a bee. The striped-tail or devil scorpion is common in homes but also has mild venom. The bark scorpion is the small, pale, slender one with thin pincers, and it is the only Arizona scorpion with venom potent enough to be a medical emergency. It is also the only one that habitually climbs and clusters, so a scorpion found high on a wall or in a group is very likely a bark scorpion.