Sydney funnel-web spider: a fatal bite for humans

Sydney funnel-web spider is known to be one of the most aggressive and venomous spiders in the world

by Lorenzo Ciotti
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Sydney funnel-web spider: a fatal bite for humans

Atrax robustus or Sydney funnel-web spider is known to be one of the most aggressive and venomous spiders in the world. Among the 40 species of the Hexathelide family it is the only one, together with Hadronyche formidabilis, whose bite is fatal for humans.

The species is one of three of the genus Atrax, present only in Australia. The original habitat of this spider was an area of ​​no more than 100 km radius from the city of Sydney, in New South Wales, but now it can also be found throughout Queensland and in some Tasmanian forests.

The first scientific study on the poison of A. robustus was carried out by Kellaway in 1934. Among other things it turned out that the toxins contained in it are not lethal to various laboratory animals, or are only so at very high doses, while the sensitivity is very high in primates and in humans.

The lethal activity is believed to depend on only one of the many components of the venom, robustoxin (δ-ACTX-Ar1), also called atraxotoxin, from the genus of spiders. It is a low molecular weight (4854 u) neurotoxic polypeptide, with a high proportion of basic amino acid residues (pH> 9), which in primates slows the inactivation of the sodium channel in motor neurons and the autonomic nervous system.

The LD50 in newborn mice is 0.16 mg / kg.

Sydney funnel-web spider: a fatal bite for humans

From 1927 to 1981, 13 documented cases of death due to Atrax bite are reported. An antidote has been available since 1981 and there have been no more fatalities.

These spiders are attracted to water and it is often possible to find them at the edges of swimming pools, where they sometimes fall. The Atrax robustus is able to survive for several hours in these baths, retaining air bubbles around it thanks to the hair and it has happened that it has bitten those who tried to take it out of the water.

Other places where the spider does not disdain to walk are, for example, the gardens of the houses. They were also found in some houses, hidden in clothes, which repeatedly bit the unsuspecting landlords. The color is dark, ranging from black, even with bluish shades, to plum and brown.

The male lives shorter and has a generally smaller body than the female, but longer legs. In both sexes, a shiny, hairless carapace covers the cephalothorax. As in the dipluridae, the seritteri are quite long. Males have a long spur protruding from the second pair of legs, used in mating.