Australasian funnel-web spider

Australasian funnel-web spiders are very dangerous spiders of the family Hexathelidae. These spiders are found in two genera of the family: Hadronyche (which is not associated with any known human fatalities) and Atrax (which is known to have killed 13 people). They are notorious for the inclusion of the Sydney funnel-web spider (Atrax robustus) native to eastern Australia. There are other genera in family Hexathelidae, but these don't have the notorious reputation of the Australasian funnel-webs.

Description

These spiders are medium-to-large in size, with body lengths ranging from 1cm to 5cm (0.4" to 2"). They are darkly colored, ranging from black to brown, with a glossy carapace covering the front part of the body. Like the related diplurid spiders, the hexathelids generally have long spinnerets; this is especially true of A. robustus.

Like other Mygalomorphae, (also called the Orthognatha an infraorder of spiders which includes the true tarantulas), these spiders have fangs which point straight down and do not cross each other (cf Araneomorphae). They have ample poison glands that lie entirely within their chelicerae. Their chelicerae and fangs are large and powerful. Although they are rather small compared to the true tarantulas, they should not be handled without taking substantial precautions because their fangs have been known to penetrate fingernails and soft shoes, resulting in dangerous bites.

Range and habitat

The primary range of the Australasian funnel-web spiders is the eastern coast of Australia, with specimens found in New South Wales, South Australia, and Queensland. In addition, some specimens have been found in other islands in the south Pacific, including Tasmania, New Guinea, and the Solomon Islands. The Atrax genus, with only one species (A. robustus) is limited to the Sydney area; the Hadronyche genus has a wider distribution.

These spiders construct a funnel shaped web and lurk for prey in the small end of the funnel. They frequently search for a place to nest under human dwellings, or under nearby rocks, logs, or other similar objects. They are most active at night. They are large, the largest being about 5 cm long, and they often bite aggressively and repeatedly. It is said that these spiders are unable to climb well because of their bodyweight. However they can move very quickly across the ground.

Medical significance

Funnel-webs are probably one of the three most dangerous spiders in the world and is regarded by some to be the most dangerous. The most-studied funnel-web, Atrax robustus, has a powerful neurotoxin known as robustotoxin that is known to cause death within a period ranging from 15 minutes (this occurred when a small child was bitten) to three days. This toxin operates by opening sodium channels. Although extremely toxic to primates, the venom appears to be fairly harmless to many other mammals, including cats and dogs which neutralise the venom totally within 30 minutes. While some very venomous spiders may give dry bites, these spiders do so much less frequently. (For a comparison of the toxicity and amounts injected of various spider venoms, see spiders having medically-significant venom.)

The female venom was thought to be only about a sixth as potent to humans as that of the male but recent research has proven that false. The bite of a female or juvenile may be serious; however, considerable variability occurs in venom toxicity between species.

Examination of bite records seems to indicate that wandering males have caused a large majority of fatal bites to humans. Most bites seem to occur when the male spiders wander about looking for receptive female of their kind for mating during the warmer months of the year.

Males, recognised by the modified terminal segment of the palp, are aggressive and tend to wander in search of females at night in summer rain. They are attracted to water and hence are often found in swimming pools where they have fallen while so engaged. They also show up in garages and yards in suburban Sydney.

There have been 26 recorded deaths in Australia in the last 100 years from spider bites, 13 of these potentially from male venomous funnel-web spiders. Most victims will have been the young, ill and infirm before antivenom was developed in 1981 through a passionate team effort led by Dr Struan Keith Sutherland (17 June 1936 - 11 Jan 2002), head of immunology at the Australian Commonwealth Serum Laboratories in Sydney. Fortunately, the antivenom is fast-acting and highly and globally effective. There have been no deaths since it became available.

90% of bites to humans from this spider are judged not serious enough to warrant administration of antivenom. However, the remaining 10% of the bites demonstrate the importance of promptly securing medical advice in case emergency treatment should prove necessary.

Members of the genus Hadronyche may also cause fatal envenomations although none have been recorded. Assays of venom from several Hadronyche species have shown it to be highly similar to robustotoxin; in some cases (such as H. formidabilis) in concentrations equal to or greater than A. robustus.

Species

The following funnel-web species have been identified:

Atrax robustus, Sydney funnel-web spider
Hadronyche adelaidensis, Adelaide funnelweb spider
Hadronyche cerberea, Tree funnelweb spider or Southern funnelweb spider
Hadronyche eyrei, Eyre Peninsula funnelweb spider
Hadronyche flindersi, Flinders funnelweb spider
Hadronyche formidabilis, Northern Rivers funnelweb spider or Northern funnelweb spider
Hadronyche infensa, Toowoomba funnelweb spider or Fraser Island funnelweb spider.
Hadronyche modesta, Victorian funnelweb spider
Hadronyche pulvinator, Cascade funnelweb spider
Hadronyche venenata, Tasmanian funnelweb spider
Hadronyche versuta, Blue Mountains funnelweb spider

See List of Hexathelidae species for a complete list of species within this family (about 90 species in 11 genera).

Images

Image:Victorian funnelweb.jpg|Victorian Funnelweb Spider Image:Victorian funnelweb02.jpg|Atrax robustus Image:Victorian funnelweb_side.jpg|Also called the Sydney Funnelweb Spider Image:Victorian funnelweb_rear.jpg|Female

References

Medical information regarding bites and geographical ranges
Main, Barbara York. 1976. Spiders. Collins, Sydney, Australia.
McKeown, Keith C. 1952. Australian Spiders. Angus and Robertson, Sydney, Australia.
Spiders. Funnel-Web Spiders. Family Hexathelidae
BBC News: Scapegoats For Diseases 6th August 2004.
Spider Myths: Ours Are Deadlier Than Yours

External links

Funnel-web spiders | Hexathelidae | Australian animals | Dangerous spiders

Atrax robustus | Hexathelidae