The secret of scorpions' success is that they burn energy extraordinarily slowly, John Lighton of the University of Nevada, Las Vegas, and his colleagues now propose
"It's as if every hectare contained one medium-sized human, cut up into scorpion-sized bits and scattered around," says Lighton, who analysed the metabolism of nine scorpion species from around the world. Scorpions use so little energy in staying alive that they have more left over to invest in new scorpions.
"It was known that scorpions had fairly low metabolic rates, but this is lower than was appreciated before," says Harold Heatwole, a specialist in desert ecology at North Carolina State University in Raleigh.
"We don't know why a gram of scorpion costs one-quarter of a gram of insect to maintain," says Lighton. "The mystery is why insects and spiders don't do the same thing."
If we could work out what it is that makes scorpion cells so efficient, we might be able to use the same trick to lower metabolic rates in human tissues. This could better preserve transplant organs, or even help humans to endure long space journeys, Lighton speculates.
Such economy comes at a price, particularly for small scorpions. Cannibalism is rife, partly because, at such high population densities, they are more likely to bump into -- and eat -- one another.
What's more, because young scorpions do not disperse over large distances, much of the cannibalism is kept in the family, with mothers eating their brood.
As Heatwole comments, it is "a reasonable idea" that by thinning out their more sluggish offspring themselves, parents recycle resources to make other, perhaps more competent, young. Lighton calls it "another chance to roll the genetic dice".
Cannibalism may also lead to an increase in the total amount of scorpion in the desert. Small scorpions eat prey that their larger brethren would not bother with, allowing the population as a whole to hoover up a greater proportion of the desert's total food supply.
By eating small scorpions, large scorpions gain indirect access to this food -- just as humans can eat grass by feeding it to cows first.
"Juvenile scorpions are an energy storage organ for the population as a whole," says Lighton. He likens them to the honeypot ants that store sugar solution in their bloated stomachs to pass on to their nestmates in hard times.
Lighton admits that many of his hypotheses are "going out on a limb", but he hopes they will stimulate other researchers into action. "I fully expect people to attack these ideas," he says, "but all of them would be easy to test."