The Red Bellied Black Snake is a venomous snake native to the east coast of Australia. It can be found in the urban forest, woodland, plains and bushland areas of the Blue Mountains, Canberra, Sydney, Brisbane, Melbourne, Cairns and Adelaide. The Macquarie Marshes marks a western border to their distribution in New South Wales. It is most commonly seen close to dams, streams, billabongs and other bodies of water, although they can venture up to 100 m away. In particular, the Red Bellied Black Snake prefers areas of shallow water with tangles of water plants, logs or debris.
Red Bellied Black Snakes have multiple places they can hide in their habitat including logs, old mammal burrows, and grass tussocks. They can flee into water and hide there, with one report of one staying submerged for 23 minutes. When swimming they may have the whole head or the nostrils above the water's surface. Within their habitat, Red Bellied Black Snakes appear to have ranges or territories that they are familiar with and generally remain within. A 1987 field study in three New South Wales localities found that they varied widely, from 0.02 to 40 hectares in size.
The Red Bellied Black Snake is generally not an aggressive species. However, when provoked, it will recoil into its striking stance as a threat, but will try to escape at the first opportunity. It is generally active by day, though nighttime activity has occasionally been recorded. When not hunting or basking it may be found beneath timber, rocks and rubbish or down holes and burrows.
Snakes are active when their body temperatures are between 28 and 31 C. They also thermoregulate by basking in warm sunny spots in the cool early morning and rest in shade in the middle of hot days, and may reduce their activity in hot dry weather in late summer and autumn. In July 1949, six large Red Bellied Black Snakes were found hibernating under a concrete slab in marshland in Woy Woy, New South Wales. Groups of up to 6 hibernating Red Bellied Black Snakes have been recorded from under concrete slabs around Mount Druitt and Rooty Hill in western Sydney.
The diet of the Red Bellied Black Snake primarily consists of frogs, but it also preys on reptiles and small mammals. They also eat other snakes, including those of their own species. Fish are hunted in water. As Red Bellied Black Snakes grow and mature, they continue to eat the same size prey but add larger animals as well. Although they prefer live food, Red Bellied Black Snakes have been reported eating frogs squashed by cars.
They are susceptible to cane toad toxins. The introduction of Cane toads in Australia dates to 1935, when cane toads (Rhinella marina) were introduced in an attempt at biological control of native beetles which were damaging sugar cane fields (a non-native plant). The intervention failed, mostly because the toads are on the ground while the beetles feed on leaves at the top of the plant. One research study concluded that in less than 75 years the Red Bellied Black Snake had evolved in toad-inhabited regions of Australia to have increased resistance to toad toxin and decreased preference for toads as prey.