Why the male Sydney funnel-web spider is significantly more dangerous than the female

Nature · Published 29 September 2026 · Updated 25 October 2026 Swipe more like this →

In short: The Sydney funnel-web spider is a venomous native of eastern Australia, feared for its potent bite. While both sexes are glossy and dark, the male is smaller, longer-legged, and far more lethal. Understanding why these spiders wander into homes is essential for safety in their moist, coastal habitat.

The Sydney funnel-web spider, Atrax robustus, is a terrestrial mygalomorph found within a 100-kilometre radius of Sydney. These spiders typically dwell in silk-lined burrows in moist, sheltered microhabitats like logs or rock crevices. While females spend most of their long lives inside these retreats, males frequently wander during warmer months in search of mates. This behavior increases the likelihood of human encounters, as males may inadvertently enter houses or fall into swimming pools, where they can survive for up to 24 hours by trapping air bubbles on their abdominal hairs.

The danger posed by these spiders is primarily linked to the male's venom. Delta-atracotoxin, the active component, is an ion channel inhibitor that is highly toxic to humans and other primates but does not affect other mammals. Male venom is significantly more potent than that of females, and there have been no documented cases of severe envenoming by female specimens. When threatened, the spider is aggressive, often striking repeatedly with large fangs. Symptoms of a bite can appear in under an hour, including muscle twitching, breathing difficulties, and severe hypotension.

Before the introduction of an antivenom in 1981, bites from these spiders were occasionally fatal. The antivenom, developed by a team led by Struan Sutherland, has been highly effective; no deaths have been recorded since its implementation. Treatment is considered a medical emergency, with dosage requirements varying based on symptom severity. In extreme cases, such as a 2017 incident involving a 10-year-old boy, as many as twelve vials have been administered. Because one dose requires approximately 70 milkings, public participation in venom-collection programs remains a vital component of maintaining the antivenom supply.

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