WASHINGTON (AP) _ Scorpions don't bother to waste venom killing a victim if they don't have to. Instead they use a prevenom that causes extreme pain, resorting to the deadlier version only when necessary, researchers have discovered.
A team led by entomologist Bruce D. Hammock of the University of California, Davis, was researching the possibility of an anti-venom for scorpions when they discovered that the stinging creatures produced two kinds of venom.
When first confronted by a threat the scorpion produces a clear liquid on its stinger, Hammock said. The more deadly venom, a thick liquid, ``like a milkshake,'' is produced later, if the threat continues.
It's a clever strategy, Hammock explained, because the deadly true venom uses a lot of proteins and peptides that are costly for the scorpion to make.
So instead it tries to get by with a faster acting and more painful toxin that doesn't kill, but is easier to make.
The findings are reported in this week's online edition of Proceedings of the National Academy of Sciences.
The first scorpion weapon, what Hammock calls a pretoxin, gets its kick largely from potassium salts that block receptors in animal cells, rapidly causing severe pain.
``I was surprised,'' at the discovery of this pretoxin, Hammock said. ``We spent years looking at the very complex, highly toxic peptide toxin ... and the idea that the scorpion was using salt was a real surprise.''
It's of more than just biological interest that through evolution the scorpion has developed a way to generate pain and frighten predators and, if necessary, to follow this with a very highly toxic peptide toxin, Hammock commented.
He said he has never seen a scorpion skip the prevenom and go directly to the more deadly attack.
Hammock's team was working with Patabuthus transvaalicus, a South African scorpion that is reportedly one of the most deadly.
He said the dual-venom release has been seen in all the scorpions his lab has worked with, but he could not guarantee that every type of scorpion does this.
Dr. Paul Fletcher of East Carolina State University, who was not part of the research team but who has studied scorpions for 25 years, said that in many animal glands that produce secretions there are separate cells to produce proteins and to produce a watery secretion to move the proteins out.
``The stinging process may be such that first comes the liquid and the business end of venom comes later,'' he commented. ``That makes their publication interesting and valuable to the scientific community.''
Hammock said he got interested in working with scorpion venom while researching insecticides. He wanted to take the type of common cold virus that infects insects and insert a gene for a toxin, so that when the insect gets a cold it dies.
In the process he came across the deadly P. transvaalicus, with a toxin that turned out to be selectively toxic to mammals. That ruled it out for his insect work, but led to the attempt to develop an anti-venom.