Stephens's banded snake (Hoplocephalus stephensii) is a species of highly venomous tree snake in the family Elapidae. The species is endemic to Australia.
Taxonomy Gerard Krefft described Hoplocephalus stephensii as a species new to science in 1869. The specific name stephensii, is in honour of Australian academic William John Stephens.
Description H. stephensii grows up to 1 meter (39 inches) in total length (including tail), with some specimens having been recorded as having a total length upwards of 120 cm (47 in). The Stephens' banded snake is the largest species within the genus Hoplocephalus, weighing up to 250 g (8.8 oz) as an adult. On average, females of this species are larger than males. This slight sexual dimorphism is an adaptation that likely improves the reproductive capabilities of females. The anterior scalation of Stephens's banded snake consists of 21 rows of midbody dorsal scales, and 220 to 250 ventral scales. Posteriorly, its singular subcaudal scales can range between 50 and 70 scales from the anal plate to the tip of the tail. This species has a singular (undivided) anal plate that covers its cloacal opening. The ventral scales of the genus Hoplocephalus differ from other elapids as they have lateral notches along the caudal border of each of these scales. This adaptation aids with gripping onto branches whilst climbing. Additionally, the occipital scales on the head of this snake are elongated. The body of the Stephens's banded snake is adorned with alternating grey or black and dirty-white bands of colouration on the dorsal side of the snake. These snakes may have over 40 of each colour band from the back of the head to the tip of the tail. Whilst the flat and quadrangular belly of the snake is mostly dirty-white with occasional splotches of grey towards the head and tail end of the snake. The top of this species' head is typically dark brown in colouration, and it has pale blotches or bars of patterning along the lips. The morphological composition of a slender body and broadened arrow-shaped head also allows for more agile locomotion in an arboreal habitat whilst also having the capability of predating on a large range of species within the ecosystem. This unique body plan essentially reduces metabolic costs, allowing the snake to retain energy for longer periods of time.
Distribution and habitat The Stephens's banded snake is endemic to the east coast of Australia. The distribution of this snake spans from its northern most range in the Kroombit tops of south-eastern Queensland down to the Gosford Area of New South Wales. Within this coastal range, the species is typically restricted to high-rainfall remnant forest regions, secluded from human intervention. The Stephens's banded snake can be found up to an altitude of 950 m (3,120 ft) above sea level within its geographical range. Studies on the habitat preferences of this species have found that it prefers to reside around 20 m (66 ft) high in canopy trees. H. stephensii has a broad tolerance for variations in abiotic and biotic factors such as vegetal communities and climatic changes within the constraints of its remnant forest habitats. The species will favour areas with less rugged terrain as well as hollow bearing trees, dense understory vegetation or rocky outcrops that it may utilise to seek refuge. Individual male Stephens's banded snakes occupy an average home range of 20.2 hectares (49.9 acres). Whilst the females of the species have a much smaller average home range of 5.4 hectares (13.3 acres). This difference is likely due to the fact that males may venture out of their typical territories in order to find a viable mate.
Behavior Stephens's banded snake has been described as having a nervous and defensive temperament towards other animals. This species of snake is a relatively solitary animal, only voluntarily interacting with other individuals of the same species during mating season, in which males will actively pursue females to reproduce. If females are apprehensive to reproduce upon the pursuit of potential mates, they may assume a stereotypical posture that is used to prevent males from engaging in copulation. The female will form a tight coil with its body, with its vent in the centre coil, out of reach from the male. Stephens's banded snake is one of the few predominantly arboreal elapid species in Australia. Other Australian elapidae that exhibit similar arboreality include the broad-headed snake and the pale-headed snake, both of which belong to the genus Hoplocephalus. Stephens's banded snake is also capable of living a terrestrial lifestyle depending on the available resources in its environment. The species is nocturnal; thus, it spends a large portion of the day sequestering in the canopy tree hollows within the mesic forests in which it resides. The Stephens's banded snake displays significant reluctance with its heliothermic behaviours. Due to its small size it is at risk of predation. Therefore, this snake will spend minimal time basking amongst the branches of trees. Typically, it is semi-covered by foliage so as to offer some means of concealment whilst in this vulnerable position. A study on the basking behaviours of H. stephensii has revealed that the species only prefers to overtly bask when it is either in late stages of pregnancy, has just fed, or is in the process of undergoing ecdysis. Throughout the winter season, Stephens's banded snake stops feeding and undergoes brumation in the protection of a tree hollow for up to five months. During this period of time, its metabolism is significantly slowed, allowing it to conserve energy. Being cold blooded, it is only able to resume digestive processes when temperatures rise again in its environment. Studies on the survivable temperature threshold of this snake have revealed that its body temperatures may fluctuate anywhere between 11.1 °C (52 °F) to 37.8 °C (100 °F) depending on the climatic conditions. The typical diurnal body temperature of this snake species averages at 28.4 °C (83 °F). The species is at its most active in its natural habitat in the months of September to May. Stephens's banded snake is highly vagile and may use up to 30 different trees within its range. Territories of individuals may overlap. Despite this, it avoids conspecific encounters.
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