Scorpions produce not only a venom to immobilize their prey and ward off predators but also a chemically distinct prevenom, report researchers at the University of California, Davis.

The prevenom, which is biologically easier for the scorpion to produce and more effective at paralyzing prey, may be useful in biological pest control.

"It appears that scorpions use the rapid and more efficient prevenom initially for quick defensive maneuvers, and then switch to the more potent venom if the threat persists," said Bruce Hammock, a UC Davis entomologist and an authority on biological pest controls. The prevenom findings by graduate student Bora Inceoglu and fellow researchers are reported in the Jan. 27 issue of Proceedings of the National Academy of Sciences.

All of the 1,250 known scorpion species produce some type of venom, delivered by the stingers located at the tips of their tails. However only 25 to 50 of those species secrete venom that is considered medically important. For most species, the venom is simply a very successful tool for immobilizing their prey and scaring off predators.

The venom is composed of water, salts, small molecules, peptides and proteins. The peptide toxins are the most active compounds in the venom. Previous studies have suggested that venom is used sparingly and that the scorpion is able to regulate secretion of its venom.

Working with a South African scorpion, Parabuthus transvaalicus, the researchers noticed that the first droplet of venom secreted by each scorpion was different to the remainder of the venom. For example, that first drop was transparent, while the subsequent secretions of venom were opalescent and more viscous.

While the scorpion venom contained at least 100 different peptides, the prevenom contained only three major peptide groups, which were also present in the venom. Furthermore, the prevenom contained six times less protein than venom, but a 16-times higher concentration of potassium.

Rather than using peptides, which are complicated to produce, the scorpion was using simple potassium ions to upset the body chemistry of its victims.

The prevenom works more quickly in paralyzing insects and in causing pain in mammals, but the venom is more lethal against both.

Hammock is interested in harnessing the mechanisms observed in scorpion toxins for use in controlling agricultural pests.