3. Australian Brown Snake
Source: Iconosquare
While the brown snake is only the second most venomous snake on Earth, it makes up for this with huge populations. They are big, fast and extremely aggressive. They possess a powerful neuro-toxin which will cause respiratory failure and hemorrhaging. They are also difficult to identify. They come in many shades of brown and a variety of shapes. So, if you see a snake while in Australia, just run.