Desert Scorpion
Scorpions are one of the most ancient groups of land animals on Earth, having existed for over 400 million years (longer than the dinosaurs). They are common in deserts all around the world, where their tough exoskeletons help them survive heat and dryness. Desert scorpions hunt at night, ambushing insects, spiders and even small mice. They glow eerie green under ultraviolet light, a feature that still puzzles scientists.
- Number of speciesapprox. 2,500 worldwideapprox. 100 dangerous to humans
- Age of scorpions430 million yearsOlder than dinosaurs
- BiggestEmperor scorpionapprox. 23 cm long, lives in Africa
- Most dangerousDeathstalkerLives in North Africa and Middle East
- Lifespanapprox. 6 to 25 yearsLong-lived for an arthropod
- Strange featureGlows green under UV lightScientists still puzzled why
How big can scorpions get?
The African emperor scorpion is the biggest. The deadly deathstalker is medium-sized but is the most venomous.
What is a scorpion?
A scorpion is an eight-legged arthropod (a relative of spiders, mites and horseshoe crabs). All scorpions share the same basic body plan: a pair of pincers (called pedipalps) at the front for grabbing prey, four pairs of legs for walking, a segmented body, and a long curving tail tipped with a venomous stinger. Scorpions can range from tiny (less than 1 cm) to over 20 cm long.
How do scorpions survive in the desert?
Scorpions are remarkably well-adapted to desert life:
- Tough exoskeleton. The waxy outer skin of a scorpion is highly waterproof, keeping water inside the body.
- Hide by day. Almost all scorpions are nocturnal, hiding under rocks, in burrows or in crevices during the heat of the day.
- Slow metabolism. Scorpions can slow their metabolism to extremely low levels, surviving for months without food.
- Get water from food. Like most desert hunters, scorpions get most of their water from the bodies of their prey.
- Tolerate extreme conditions. Some desert scorpions can survive being frozen overnight in cold deserts, or temperatures over 45 °C in hot ones.
How dangerous are they?
Of around 2,500 scorpion species, only approx. 25 are considered seriously dangerous to humans. The most dangerous include the deathstalker of North Africa and the Middle East, the Arabian fat-tailed scorpion, and the Brazilian yellow scorpion. Their venom contains a mix of nerve toxins that can cause severe pain, paralysis, breathing difficulties and (in rare cases) death.
Most scorpion species, however, have a sting roughly comparable to a bee or wasp. The huge African emperor scorpion looks terrifying but has a mild sting and is popular as a pet. As a rule, the bigger the pincers, the milder the sting (because the scorpion catches its prey by crushing rather than stinging). The most dangerous scorpions tend to have small pincers and powerful stings.
Scorpion reproduction
Scorpions have unusual reproduction. The male leads the female in a kind of courtship dance in which the pair clasp pincers and walk in slow circles. The male then deposits a sperm packet on the ground and manoeuvres the female over it. Female scorpions are unique among arthropods in that they give live birth rather than laying eggs. The tiny baby scorpions ride around on their mother's back for the first few weeks of their lives, getting off only after their first moult.
Deeper dive: scorpion fluorescence, ancient ancestry, and venom medicine
The mystery of scorpion fluorescence is one of the more entertaining unsolved problems in biology. Under ultraviolet light (such as moonlight or a black-light torch), all scorpions glow a bright cyan-green colour. The glow comes from chemicals in the outer waxy layer of the cuticle (the scorpion's skin). When a scorpion sheds its skin, the new skin is initially non-fluorescent and only develops the glow as the chemicals build up over the following days. Several hypotheses have been proposed for why scorpions glow: protection from UV radiation, attracting prey, confusing predators, communication with other scorpions, or simply a chemical accident. The most recent research suggests scorpions may use their fluorescence as a kind of "whole-body light meter" to find shelter; on bright moonlit nights when predator risk is high, scorpions remain hidden more than on dark nights, and the fluorescence may help them detect the ambient light level.
Scorpions are among the most ancient land animals. The oldest known scorpion fossil dates from approx. 437 million years ago, in the Silurian Period. Early scorpions were aquatic, similar to modern sea scorpions and horseshoe crabs. They were among the very first animals to colonise land, possibly as long as 430 million years ago, well before the first amphibians, reptiles or dinosaurs. Despite all the changes the Earth has gone through (mass extinctions, ice ages, the breakup of supercontinents), scorpions have survived almost unchanged. Modern scorpions look very similar to their 300-million-year-old fossil ancestors. This is partly because their body plan is remarkably well-suited to ambush predation on small prey, a niche that has remained stable through all the changes around them.
Scorpion venom has become one of the most studied natural pharmacological sources on Earth. Scorpion venom contains a complex mixture of dozens to hundreds of different small proteins called peptides, each of which targets specific ion channels in the nerve and muscle cells of prey. Different scorpions have venoms tailored to different prey types: some are more effective against insects, others against mammals. This specificity makes scorpion peptides valuable for medical research, because they can selectively affect specific cell types without harming others. Chlorotoxin from the deathstalker scorpion is being developed both as a brain-cancer imaging agent and as a potential cancer treatment. Other scorpion peptides are being studied for treating autoimmune diseases, irregular heart rhythms, and pain.
For other desert animals, see desert animals. For desert ecosystems generally, see desert ecosystems.