The spider responsible for the most fatalities, is the black widow. As far as potential danger, the Australian funnelweb spider. The Brazilian wandering spider has the most lethal venom, but you are far more likely to encounter the funnelweb spider. likewise, you are far more likely to encounter a widow spider. the black widows venom is 15 times more lethal than the rattlesnake.
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A rock spider.
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It is the Black Widow spider. :)