Australian Funnel-web Spider - Medical Significance

Medical Significance

Sydney funnel-webs are one of the most dangerous spiders in the world and are regarded by some to be the most deadly.

Examination of bite records has implicated wandering males in most if not all fatal funnel-web bites to humans. Adult males, recognised by the modified terminal segment of the palp, will defend themselves vigorously if they feel threatened and tend to wander during the warmer months of the year looking for receptive females for mating. They are attracted to water and hence are often found in swimming pools, into which they often fall while wandering. The spiders can survive such immersion for several hours and can deliver a bite when removed from the water. They also show up in garages and yards in suburban Sydney. Contrary to a commonly held belief, no funnel-web spider is able to jump, although they can run quickly.

While some very venomous spiders may give dry bites, these spiders do so much less frequently. An inefficient mode of delivery (to large animals) and interrupted contact are also possible causes of low volume delivery. It has been claimed that approximately 10% to 25% of bites will produce significant toxicity but the likelihood cannot be predicted and all should be treated as potentially life-threatening. Funnel-webs are not normally aggressive but will defend themselves vigorously if frightened or threatened. During an attack the funnel-web spider generally maintains a tight grip on its victim and bites repeatedly, making it an especially traumatic experience for humans who are bitten and increasing the risk of severe envenomation.

There have been 27 recorded deaths in Australia in the last 100 years from spider bites. Bites from Sydney funnel-web spiders have caused thirteen deaths (seven in children). In all cases where the sex of the biting spider could be determined, it was found to be the male of the species. Most victims were young, ill or infirm. One member of the genus Hadronyche, the northern tree funnel-web has also been claimed to cause fatal envenomation but, to date, this lacks the support of a specific medical report. Assays of venom from several Hadronyche species have shown it to be similar to Atrax venom.