Funnel-web Spiders

Funnel-web Spiders

Funnel-webs are the subject of fear, fascination and myth. They are a group of Australian spiders belonging to the family Hexathelidae. They include some of the most venomous spiders on the planet and are generally shiny black spiders with a relatively sinister appearance.

Sydney Funnel-web

Despite there being around 40 species, the most well know and notorious species is the Sydney Funnel-web (Atrax robustus). Prior to the development of the antivenom in 1980, 13 human deaths were attributed to the males of this species. Male Sydney Funnel-web have a component in their venom which the females lack. This toxin known as Robustoxin (d-Atracotoxin-Ar1) is the chemical that makes these spiders so dangerous to humans. For some unknown reason, this chemical affects primates (humans and our relatives the monkeys and apes) severely, but has relatively little effect on other mammal species. The other unfortunate part of this equation is that Australia’s most populated city was founded in the heart of this spiders’ natural habitat. Despite the distribution of these spiders and toxic venom, since the development of the antivenom the real danger of these spiders has greatly diminished. There have been no deaths as a result of Sydney Funnel-web bites in 35 years, yet the fear of these spiders remains extraordinarily high within Australia. It is certainly a case where the perceived danger far outweighs the real risk, and some perspective is required. Few people fear motor vehicles which have caused almost 70,000 deaths in Australian within the same 35 year period.

Aggressive Sydney Funnel-web

A Sydney Funnel-web (Atrax robustus) in a defensive pose.

 

Victorian funnel-web

Victorian Funnel-web (Hadronyche modesta)

 

Funnel-web spiders are ambush hunters and live within silken retreats either underground, or in the case of a few species, within hollows and crevices in trees. The majority of species are found in relatively moist habitats such as shaded gullies in forested areas. Species are spread from South Australia (Adelaide Hills) through areas of Victoria, Tasmania and up the east coast into Queensland. They Sydney Funnel-web (Atrax robustus) is confined to radius of about 160km around Sydney itself. Most ground dwellers will occupy naturally occurring spaces beneath rocks and logs, and line the interior with silk. Many species have multiple entrances which are tube-like openings of silk, usually with some distinct silk strands (trip lines) connected to them. These lines alert the spider of the presence of prey when they are hunting. Insects, spiders and small vertebrates such as lizards and frogs are taken by funnel-web spiders. The prey is simply ambushed and overpowered, bitten and dragged back inside the retreat to be consumed.

Funnel-web spider in its burrow

A funnel-web in a hunting position at the entrance to its retreat.

 

Funnel-web distribution maps

The approximate distribution of funnel-web spiders within Australia. The Sydney Funnelweb (left) and the various funnel-web species together (right).

 

Regardless of their fearsome reputation, in nature these spiders don’t have it all their own way. They have their share of predators, even some which will take them on within their lairs. Centipedes are expert funnel-web predators, and will readily enter the retreat, attack and consume the occupant. Outside their retreat, funnel webs are far more vulnerable and wandering spiders have a whole spectrum of hungry animals quite willing to deal with them. These include birds, small mammals and reptiles.

The fangs of a Sydney Funnel-web

A close-up of a Sydney Funnel-web with the fangs exposed.

 

Funnel-web spiders are super-sensitive to vibrations in order to hunt in the manner they do. Approaching human footsteps are usually enough to send these spiders scurrying deep back inside their secure homes. They are certainly not looking to take on anything our size. Human encounters are usually as a result of people digging the spiders up accidentally, or with male spiders that are roaming looking for mates during the breeding season.

 Funnel-web Quick Facts

  • There have been no recorded deaths from funnel-web bites for over 35 years.
  • Funnel-webs cannot jump – they can only rear up and strike downwards.
  • Funnelwebs dehydrate quickly – they cannot survive for longer than a day or two indoors.
  • Funnelwebs can survive on very little oxygen and take a long time to drown.
  • There are around 40 species of funnel-webs currently classified.
  • Most other funnel-webs’ do not have venom as toxic as the Sydney Funnel-web (Atrax robustus).
  • Sydney Funnel-webs are not spreading throughout Australia.
  • The venom of Atrax robustus does not severely affect cats, dogs or native Australian mammals.

Further reading

http://australianmuseum.net.au/funnel-web-spiders-group

 

All images copyright © Alan Henderson

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