Why funnel-web spiders are so dangerous to people

FUNNEL-WEB spiders have a fearsome reputation. People bitten by these Australian arachnids suffer extreme pain, breathing problems, confusion, convulsions and dangerously high blood pressure. Left untreated, the venom can kill within hours. For years, researchers assumed this lethal effect was an evolutionary accident. The venom, they presumed, evolved to help the spiders kill their prey—normally insects. Killing mammals was either just collateral damage or a form of protection against possible predators.Except that the venom does not, in general, kill mammals. Dogs, cats, mice, rabbits and guinea pigs all shake it off. It is only human beings and other primates that succumb. And there is another odd thing about it. Funnel-web-spider venom has thousands of components, but delta-hexatoxins, the specific molecules within it that kill people, are produced in particularly large quantities by sexually mature males during the breeding season—a time when they are barely feeding at all.