What spider has the most deadly bite?

What's the Most Venomous Spider? The Brazilian Wandering Spider (Phoneutria nigriventer) has such a strong venom that only 0.006mg will kill a mouse.

What are the Most Deadly Spiders?
Of the 35,000 species of Spiders, only 27 species are known to have caused human fatalities. In the USA their is the Brown Recluse (Loxosceles reclusa) and the Black Widow (Latrodectus hesperus). The venom of a Black Widow spider is 15 times as toxic as the venom of a prairie rattlesnake. The bite from a black widow spider is not automatically fatal. In fact, less than 1% of all people bitten by this spider run the risk of dying, and most of them are saved with the use of antivenin.