Brazilian wandering spider

:  any of a genus (Phoneutria) of large, venomous, nocturnal spiders of tropical South America that do not build webs and actively hunt prey by traveling on the ground ◆Brazilian wandering spiders adopt a characteristic aggressive defense posture in which their front legs are raised straight up into the air. Along the way we meet some scary hairies, among them a Brazilian wandering spider, the most dangerous spider in the world, we're told, with venom 18 times as potent as a black widow's … — Chip Crews, Washington Post, 11 Feb. 2006 —called also banana spider