By Vladimir Hernandez
Their investigation follows reports that men bitten by the Phoneutria nigriventer experienced priapism - long and painful erections.
A two-year study has found that the venom contains a toxin, called Tx2-6, that causes erections.
Further tests are being carried out in the US before the substance can be approved for human use.
The results, from the Medical College of Georgia, are expected in a month's time.
The bite of Phoneutria nigriventer, known as the Brazilian wandering spider, is potent and can be deadly in some cases.
The Brazilian and US researchers interviewed men who claimed their sex lives had improved after a spider attack.
The relevant toxin identified in the venom has been tested successfully on other animals.So far, scientists believe that combining a version of the spider's venom with an existing drug for erectile dysfunction - such as Viagra, Cialis or Levtra - could produce better results.