The Sydney funnelweb spider (Atrax robustus) is a species of venomous mygalomorph spider native to eastern Australia, usually found within a 100 km (62 mi) radius of Sydney. It is a member of a group of spiders known as Australian funnelweb spiders. Its bite is capable of causing serious illness or death in humans if left untreated.

The Sydney funnelweb is medium to large in size, with body length ranging from 1 to 5 cm (0.4 to 2 in). Both sexes are glossy and darkly coloured, ranging from blueblack, to black, to brown or darkplum coloured. The carapace covering the cephalothorax is almost hairless and appears smooth and glossy. Another characteristic are fingerlike spinnerets at the end of their abdomen. The shorterlived male is smaller than the female, but longerlegged. The average leg length for the spider in general is six to seven centimeters

Sydney funnelweb spiders are mostly terrestrial spiders, favouring habitats with moist sand and clays.
Distribution is centred on Sydney, extending north to the Central Coast and south to the Illawarra region, and west to the Blue Mountains in New South Wales.

The spider can be found in moist microhabitats, including under logs and foliage.

They typically build silklined tubular burrow retreats with collapsed "tunnels" or open "funnel" entrances from which irregular triplines radiate over the ground. In some exceptions, which lack triplines but may have trapdoors, the silk entrance tube may be split into two openings, in a Y or T form. The spiders burrow in sheltered habitats where they can find a moist and humid climate; for instance under rocks, logs or borer holes in roughbarked trees.[10][13] The longlived female funnelweb spend most of the time in their silklined tubular burrow retreats. When potential prey, which includes insects, lizards or frogs, walks across the triplines, they rush out, subduing their prey by injecting their venom.[10][13]

Males, recognized by the modified terminal segment of the palp, tend to wander during the warmer months of the year, looking for receptive females to mate with. This makes encounters with male specimens more likely as they sometimes wander into backyards or houses, or fall into swimming pools. The spiders can survive such immersion for up to twentyfour hours, trapping air bubbles on hairs around their abdomen. Sydney funnelweb spiders are mainly active at night, as typical daytime conditions would dehydrate them. During the day, they seek cover in cool, moist hideaways. After heavy rain, spider activity is increased as their burrows may be flooded.When threatened or provoked, funnelweb spiders will display aggressive behaviour, rearing up on their hind legs and displaying their fangs. When biting, the funnelweb spider maintains a tight grip on its victim, often biting repeatedly