Spider

In 2010, the Brazilian wandering spider was named in the Guinness World Records as the most venomous spider in the world. It is also aggressive, obviously making the chance of a bite from it more likely. It has a highly potent neurotoxin that can lead to breathing problems then asphyxiation and death in those bitten. Another effect of its venom is priapism, meaning erections that last a long time – hours to days – and can result in permanent impotence. However, the venom is being studied as a possible fix for erectile dysfunction. The spider only needs to inject 6 ug of its venom to kill a 20-gram mouse, and a full venom load is 1.069 mg. Death in humans has been known to occur even after antivenom has been administered.