Invertebrates
Scorpion
Scorpiones · also called scorpions
A scorpion is one of the oldest designs still walking around. Pincers in front, a stinging tail arched over the back, a flat armoured body built to slide under a rock — the shape turns up in fossils more than 400 million years old and has needed almost no revision since. Shine an ultraviolet light on one at night and it lights up blue-green.
Overview
Scorpions are the order Scorpiones, around 2,500 species, on every continent except Antarctica and most diverse in warm, dry regions. All are arachnids — relatives of spiders and ticks — with four pairs of walking legs, a pair of grasping pincers, and a segmented tail ending in a venomous sting. All are carnivores that hunt other invertebrates by ambush.
Venom and pincers
The sting is at the tail tip, not in the pincers. As a rough rule, species with big powerful pincers crush their prey and have mild venom, while species with thin pincers rely on potent venom — which is why the small, slender-clawed members of the family Buthidae include nearly all the dangerous ones. Only about 25 to 30 species can seriously harm a person.
Built to wait
Scorpions have an extraordinarily slow metabolism. They can breathe once every few hours, drop their energy use far below that of comparable animals, and survive 6 to 12 months on one meal — an adaptation to deserts where prey is scarce.
The glow, and live young
Compounds in the cuticle make scorpions fluoresce under UV, a gift to field biologists and possibly a way for the animal to judge how dark the night is. Scorpions give birth to live young, and the pale babies ride on the mother’s back until their first moult hardens them.
Status
Scorpions as a group are Not Evaluated. Most are common, but many have tiny ranges — a single cave or dune field — and are vulnerable to habitat loss, and heavy pet-trade collection led to the emperor scorpion being placed on CITES to limit its export.
Scorpion: common questions
How dangerous is a scorpion sting?
For most species, not very. Around 2,500 scorpion species exist, and only about 25 to 30 have venom capable of killing a healthy adult, nearly all of them in the family Buthidae with slender pincers and a thick tail. A sting from a typical scorpion causes intense local pain, swelling, and numbness that fades over hours, much like a bad wasp sting. A sting from a dangerous species such as the deathstalker, an Indian red scorpion, or a fat-tailed scorpion can cause a racing heart, muscle spasms, breathing difficulty, and, particularly in young children, death without treatment. Antivenom exists for the important species, and serious cases need hospital care.
Why do scorpions glow in the dark?
They do not glow on their own, but they fluoresce brightly when ultraviolet light shines on them, giving off an eerie blue-green. The effect comes from chemicals, including beta-carboline and a coumarin, in the thin waxy hyaline layer of the exoskeleton, which absorb UV and re-emit it as visible light. Freshly moulted scorpions do not fluoresce until the new cuticle matures. Why it evolved is still debated, with ideas including helping the scorpion judge light levels so it stays hidden when the moon is bright, confusing or attracting prey, or protecting against UV damage. For field biologists it is simply invaluable, since a UV torch turns an invisible desert night into one dotted with glowing scorpions.
What do scorpions eat and how do they hunt?
Scorpions are ambush predators of other invertebrates, mainly insects, spiders, and smaller scorpions, with the biggest species occasionally taking small vertebrates. Most sit at or just inside a burrow entrance and wait, detecting the vibrations and air movement of passing prey through fine sensory hairs and slit organs in the legs. When prey is close the scorpion grabs it with the pincers, and whether it also stings depends on the struggle and the species, since stinging costs venom that is slow to replace. Prey is then crushed and mashed by the pincers and mouthparts while digestive juices liquefy it, and the scorpion sucks up the resulting broth, discarding the hard parts.
Do mother scorpions really carry their babies?
Yes, and it is one of the most distinctive things about the group. All scorpions give birth to live young rather than laying eggs. The newborns, called scorplings, are white, soft, and helpless, and immediately climb onto the mother's back, where they cling in a mass for days to a couple of weeks. They do not feed during this time, living off yolk reserves, and they remain until their first moult hardens their cuticle enough for them to survive and hunt alone, at which point they disperse. A female carrying twenty or more young on her back is a common sight where scorpions are studied, and she becomes more defensive during this period.