The venom of Atrax robustus contains delta-hexatoxin, a peptide that slows the inactivation of sodium channels in nerve terminals. The result is uncontrolled firing: sweating, salivation, muscle twitching, racing heart and, in severe cases, pulmonary oedema. Symptoms can begin within minutes.
Primates, including humans, are unusually sensitive. Many other mammals, among them rabbits and cats, tolerate doses that would be lethal to a person, which is one reason the toxin's potency looks so disproportionate to the insect prey the spider actually eats. Male venom is several times more toxic than female venom, and it is wandering males that people meet.
An antivenom developed at the Commonwealth Serum Laboratories entered use in 1981. Thirteen deaths are recorded before that date and none afterwards. The supply depends on the public catching live spiders for a milking programme, and on first aid by pressure immobilisation while a patient reaches hospital.