The Adders, snakes that were not mutated extensively by the t-Virus, are not part of Umbrella's research, but rather native snakes within the Arklay Mountains that were infected by the outbreak caused by James Marcus. A significant number of Adders appeared within the courtyard area of the Arklay Laboratory, showing they favored moist regions. Their venom was greatly strengthened by the t-Virus, which can also be spread through said poison. This and the increased aggressiveness, however, were the only symptoms of the t-Virus the adders displayed. Compared to the Yawn, which was created through research carried out by Umbrella, the Adders are a minor threat at best.