Where can you find the most dangerous spider in the world?

Answer 1

"Most dangerous" is up to some debate, or at least discussion.

The venom of the black widow spider (found mainly in North America), while stronger than that of most spiders, is not as strong as that of some other species. An untreated black widow bite only results in death to an adult human in about 5% of cases. However, the black widow is fairly widespread and its territory overlaps a lot with that of humans, so worldwide more deaths are caused by black widow bites than any other kind of spider. That makes it a strong candidate for "most dangerous".

Closely related (in the same genus, Lactrodectus) to the black widow are the redback spider of Australia and the Mediterranean black widow which has a range from Portugal to Central Asia (mainly along the Mediterranean coastal region).

Brazilian wandering spiders (found, naturally enough, in Brazil, but also in tropical South America generally and sometimes in Central America) are in the genus Phoneutria, which is Greek for "murderess". They have possibly the most potent venom of any spider. They're large (for spiders), aggressive, and active (hence the "wandering" ... they actively hunt prey, and are more likely to come into contact with humans than a species that simply hides in its lair and waits for prey to come to it). However, they cause relatively few fatalities compared to Lactrodectus.

Finally, there's the Australian funnel-web spider (found in Australia, duh), a group of closely related genera, at least one species of which (Atrax robustus) produces a venom potentially fatal to humans and which is stronger than that of Lactrodectus species (though not as strong as Phoneutria). They aren't as aggressive as Phoneutria, but they will bite if threatened, and the males may wander over large areas looking for a mate (most funnel-web bites where the sex of the spider has been positively identified have been from males). Still, the relatively limited overlap of their territory with that of large human populations (and the fact that their fangs aren't adapted specifically for biting larger animals) means they don't cause many human deaths.

Overall, I personally would say the winner in the "most dangerous" contest is the black widow, so the answer to 'where' is "North America" (and Australia, if you include the redback, and the Mediterranean region, if you include Lactrodectus tridecemguttatus).

Answer 2

The most venomous spider in the world, The Brazilian wondering spider.