Distribution

Southeastern Australia.

Atrax spp.: the extreme east of Victoria and southeastern New South Wales
Atrax robustus: within a radius of about 160 km around Sydney
Hadronyche spp.: eastern Tasmania, eastern and southern Victoria, eastern New South Wales, the extreme southeast of Queensland.

a

b

Fig. 4.39 Atrax robustus
a Appearance. Characteristic for the male animals are the spurs on the 2nd pair of legs.
b Carapace: note the arrangement of the 8 eyes.

Biology

Sturdy body with massive venomous fangs. Body length in A. robustus up to 4 cm (female animals) or up to 2.5 cm (male animals). Shiny black, hairless cephalothorax (head and thorax). Posterior part of the body without markings, dark blue to dark purple in males, pale in females. 8 eyes closely grouped. 2 prominent spinnerets which are located underneath the end of the abdomen.

In Queensland these spiders prefer damp rainforest as their habitat, whereas in the more southern parts of their distribution area they are chiefly found in the drier eucalyptus forests. They build their funnel-shaped webs in hollows in the ground, cracks in rocks etc. Atrax robustus, the medically most important species, are brought into urban areas of Sydney with firewood and establish themselves quite happily close to human habitations.

Compared to the females, which hardly leave their burrow, the males wander, in particular during mating season in summer, in search of a female to mate with. During their wandering they may enter houses. When threatened they can be very aggressive and assume a defensive posture in which they raise their front pair of legs and their fangs.

Risk

Although in the majority of cases of envenoming there are no systemic effects, since the first reported fatality from the year 1927 there have been at least 12 more fatal cases of envenoming caused by Atrax robustus. Roughly half of the patients were children under 10 years. In the cases where the spider could be identified, it was always a male animal. This is a great exception among spiders, as it is generally the females that are of medical importance among the other dangerous species of spiders. Male A. robustus are easy to recognise from the spurs on the second pair of legs (Fig. 4.39). Their function is associated with the mating ritual.

Humans and apes are particularly sensitive to A. robustus venom. In contrast, cats, rabbits and toads show barely any signs of envenoming even with high doses of venom.

Hadronyche formidabilis and Hadronyche infesa are also considered potentially dangerous, perhaps also other species of this genus.

Literature (biological)

Gray and Sutherland 1978, Gray 1987, Sutherland 1978, 1983, Raven and Gallon 1987b, Raven and Churchill 1988, White et al. 1995

Australian Museum