Researchers have uncovered a natural Viagra-like chemical in the venom of a Brazilian 'wandering' spider, Phoneutria nigriventer. Kenia Pedrosa Nunes, Romulo Leite and colleagues, from the Medical College of Georgia, followed up on anecdotal reports that male victims bitten by the spiders subsequently developed a sustained erection. Analysing the components of the venom one by one they uncovered a small protein, known as Tx2-6, capable of recreating the effect in male rats. Tests on the animals shows that the protein works in a novel way compared with drugs like Viagra; it boosts the levels of an important vascular signalling molecule called NO (nitric oxide), which causes bloods vessel to relax and open up. It might therefore hold the key to managing a range of vascular disorders as well as impotence. The scientists also suggest that if given with other drugs, like Viagra, it could help to magnify their effect. According to Leite, "the combination of the two drugs could be even more efficient in patients that don't respond well to Viagra".