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 ::The definition of large tropical spiders as aggressive is based largely on human perception. In practice, most spiders are not inclined to envenomate unless they feel threatened. The claim that Brazilian wandering spiders and Sydney funnel-web spiders will attack a human without warning is unfair and largely inaccurate. In most cases (eg  ) the human disturbed the spider by accident, causing it to envenomate. Humans are correctly advised not to approach or provoke Phoneutria or Atrax, because they will perceive it as a threat and will not run away when challenged.  "