The Brazilian Wandering Spider is fast, aggressive, and noted as being the most poisonous of any spider.

According to Wikipedia,

At deadly concentrations, this neurotoxin causes loss of muscle control and breathing problems, resulting in paralysis and eventual asphyxiation.

That’s scary, but it gets weirder…

Aside from causing intense pain, the venom of the spider can also cause priapism in humans. Erections resulting from the bite are uncomfortable, can last for many hours and can lead to impotence.

However, on the bright side…

A component of the venom (Tx2-6) is being studied for use in erectile dysfunction treatments.