By Antonio de la Jara

SANTIAGO, June 1 (Reuters) - Scientists have discovered a potentially marketable contraceptive in the venom of Chile's black widow spider, whose bite is fatal to many but can also cause prolonged, painful and involuntary erections in men.

The venom of the Latrodectus mactans, a variety of black widow found only in the south of Chile, has spermicidal properties not found in black widows in other regions of the world, Chilean Dr Fernando Romero said.

Romero heads a research team that has studied the spider's venom for seven years, prompted by tales of Chilean farmers who acquired superhuman virility after being bitten by the black widow.

Initial studies focused on taking extracts from the venom to treat erectile dysfunction, but they soon discovered it had a molecule that also made it an effective contraceptive.

"This is a great business opportunity, we are the creators of the spermicide," Romero told Reuters by telephone.

He said he believes the molecule's natural properties are superior to those of synthetic spermicides currently on the market.

"For us in Chile, this has opened a window of opportunity to an incredible market, since currently there are no naturally based spermicides that have the properties of this discovered molecule," Romero said.

Romero, based at the Universidad de la Frontera in the southern city of Temuco, has already applied for a patent for his erectile dysfunction medicine.

His team discovered the property after looking into Chilean folklore that describes a virile man, one known to have spectacular sexual energy or many sexual partners, as being "spider-bitten."

The Chilean black widow is also known as the wheat spider for the wheat fields it inhabits and where its farmer-victims receive their often fatal bite.

The spider's bite can kill children and the elderly, but among strong young farmers it leads to erections that can last for days and involve involuntary ejaculations.

At the end of the ordeal, the man is left sexually energized and feels physically stronger, the saying goes.

Romero said he was confident his research would be complete in a couple of years and the spermicide would become available to world markets.

"We have to make sure there are no side effects ... so that it can be used as a gel in combination with condoms, or as suppositories for women."

The research is being supported by Chilean pharmaceuticals company Andromaco <ACO.SN>.

AlertNet news is provided by