The Brazilian Wandering Spider (Phoneutria spp.) is regarded by some as the most dangerous spider in the world. It is highly venomous and kills some 5 people across the world annually.
This spider is a member of the Ctenidae family of Wandering Spiders.
This spider is called the Wandering Spider because it wanders the jungle floor, rather than residing in a lair or maintaining a web. This attribute is another reason it is considered so dangerous. In densely populated areas, Phoneutria species usually search for cover and dark places to hide during daytime, and this may occur inside houses, clothes, cars, boots, boxes and log piles; thus generating accidents when near people.
The Phoneutria not only has a potent neurotoxin, but is reported to have one of the most excruciatingly painful envenomations of all spiders due to its high concentration of serotonin.
Phoneutria spp. is actually a genus with five known similar species whose members are highly venomous and not reluctant to attack people who appear threatening.
It is thought that they inject different quantities of venom in each bite and in some cases no venom at all. However, this theory has been questioned due to lack of evidence regarding which of the five known sub species has caused the bite.
Needless to say, that if you are bitten, death is a strong possibility and you must seek medical help immediately.