The venom of the Brazilian wandering spider (Phoneutria nigriventer) can cause necrosis of the penis – essentially, the death of penis tissue – which can sometimes require amputation.

It’s a terrifying poison best avoided, yet research suggests that in smaller amounts, the venom could hold clues to the next Viagra.

The large dose of venom dished out by the spider in nature triggers erections in mammals that are very painful and that last much too long for their primary purpose. These abnormally extended boners are technically known as priapisms, and the venom adds nausea and abdominal cramps for good measure.

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Nevetherless, scientists from the Universidade Federal de Minas Gerais in Brazil have been able to develop a synthetic version of the molecule in the venom that causes the erection. It’s called BZ371A, and has now been tested with some success on mice and rats: when put into a gel and spread on the groins of the animals, erections were triggered.

These effects happen because P. nigriventer venom (and BZ371A) triggers the release of nitric oxide in the body, which in turn boosts blood flow to the genitals. Viagra works in a similar way, by making the penis more sensitive to nitric oxide as it’s released.