Brazilian wandering spider

Phoneutria is a genus of spiders which are dangerous to human beings. Their venom is more powerful, drop for drop, than other venoms. They are called "armed spiders" in Portuguese because their venom is a powerful weapon. Their body length goes from 17 to 48 mm (0.7–1.9 in). 
These spiders live in Central America and South America. They hide in the daytime and walk around looking for food at night. So in English they are called 'wandering spiders'. There are several species, and only "Phoneutria fera" can kill healthy adult humans. People who get bitten by Phoneutria spiders can be given an antivenom. In any event, their degree of toxicity has been challenged. The spiders may be able to control the amount of venom they inject.
There are about eight "species" in this genus.