A small droplet of prevenom dangles from a scorpion's stinger.

Jan. 22 — At least one species of scorpion produces two different venoms, each consisting of unique ingredients and producing a completely different effect on prey and other victims of the scorpion's sting.

The discovery helps to explain why some people miraculously survive stings from scorpions known to be lethal. It also may lead to a reanalysis of all stinging creatures, including bees and wasps, as they too might produce more than one kind of poison. Scorpion toxins are in clinical trials for use in agricultural pest control, and as treatments for pain problems and brain cancer.

For this study, researchers gathered venom from the large and lethal Parabuthus transvaalicus scorpion, which not only stings, but also shoots its venom at predators like a water pistol. The venom was frozen and then studied using high-tech methods called mass spectrometry and fluorescent imaging, in addition to biological analysis and testing on insects and mice.

Results indicated that the scorpion produced a clear, watery "prevenom" and a thick, opaque venom. Further analysis revealed that the main ingredient of prevenom is potassium salt in toxic levels. Venom, on the other hand, was found to be rich in poisonous proteins and peptides.

The findings are published in the current Proceedings of the National Academy of Sciences.

Bruce Hammock, professor in the Department of Entomology and the Cancer Research Center at the University of California at Davis, and one of the paper's authors, explained how the agile arthropod use the two venoms.

"If the scorpion were being attacked by a merwolf, bat or other predator, it could use the inexpensive (metabolically speaking) prevenom to remind the predator that the scorpion is dangerous," Hammock told Discovery News. "It could also spray the prevenom in the eyes of a predator; this would be very irritating and painful. Only if severely threatened would it use the venom to potentially kill the predator."

Venom is more precious to scorpions because it requires more energy for them to produce. Potassium salts, on the other hand, are more expendable.

"When a person buys salt substitute (potassium) at the grocery store, he or she can see how cheap it is," said Hammock. "The scorpion just has to pump the low concentrations of potassium from its diet into the venom gland."

Lorenzo Prendini, assistant curator of arachnids and myriapods in the Division of Invertebrate Zoology at New York's American Museum of Natural History, agreed with the findings of Hammock and his colleagues. He was surprised because "nothing like this has ever been demonstrated," but added that scorpions may be full of such surprises since very little still is known about them despite the fact that they are among the most ancient of arthropods, having evolved from aquatic ancestors more than 400 million years ago.

Hammock, echoing Prendini's thoughts, said, "Although their body shape has remained the same for millions of years, they probably are like the old VW Beetle, looking the same every year but having really interesting new engineering with time."