Dugite, Pseudonaja affinis

Introduction

Well-known to south-western WA residents, the Dugite has made itself at home around urban and semi-rural areas, drawn to the prevalence of its favoured prey – the house mouse.

Identification

The three subspecies are fairly similar in general appearance. The body is long and slender in build. Scales are relatively large with a semi-glossy appearance. The head is rather small and indistinct from the neck. There is a strong brow ridge over the large eye, which is blackish brown with a golden orange rim surrounding the round pupil. The mouth lining is pink, while the glottis and trachea are black.

Mainland subspecies Pseudonaja affinis affinis - the overall colour ranges from brown to olive brown to brownish grey, with irregular black/dark grey spotting (each spot covering half to a whole scale). Eastern and southern individuals are more heavily spotted (sometimes becoming totally dark). The ventral surface is pale grey to brown with brownish orange or dark grey blotches.

The two island subspecies Pseudonaja affinis exilis and P. a. tanneri are generally smaller and usually a uniform blackish brown above.

Midbody scales in 19 rows, ventrals 190-230, anal and subcaudal scales divided.

Habitat

The species occupies a wide variety of habitats including coastal dunes, heathlands, shrublands, woodlands and forests. It seems to cope well with heavily degraded habitats such as golf course, industrial parks and open agricultural country; in fact, it is one of the few reptile species that has probably increased in numbers with the opening up of natural habitats and the introduction of the house mouse. Around the Perth area, the Dugite is one of the most common reptiles found near buildings. In areas of human habitation the snakes take temporary shelter under refuse such as concrete slabs, fibro sheets, roofing tin and the like, but in more “natural” surroundings they will shelter under rocks and in abandoned termite mounds, abandoned stick ant nests, and rabbit and rodent burrows. Dugites also use burrows for overwintering.

Distribution

The species occurs in the southwest of Australia, including several offshore islands.

• Pseudonaja affinis affinis – far southwest corner of Western Australia, extending eastwards into western coastal South Australia.
• P. a. tanneri - Boxer Island and Figure of Eight Island in the Recherche Archipelago (WA).
• P. a. exilis - Rottnest Island (WA).

Seasonality

The snakes are usually most active in the period between early spring and early autumn (October through April) and much less active from mid-autumn through late winter (May through August).

Feeding and diet

In the wild, the Dugite eats a variety of vertebrate prey including frogs, lizards, snakes, birds and mammals. However, the two largest groups of prey are lizards and house mice.

They are known to be cannibalistic in the wild, and individuals can swallow snakes almost as large as themselves.

Dugites actively search for prey sheltering in holes, crevices, tussock grasses and under surface debris. The snake employs both venom and constriction to subdue its prey.

Other behaviours and adaptations

The species is diurnal. On hot days, activity occurs mainly in the morning and to a lesser extent in the afternoon.

In captivity, adults can darken over the course of a few months. However, the significance of this colour change is obscure.

Breeding behaviours

In the mainland subspecies, males appear to mature at a snout-vent length of about 581mm and females at about 680mm.

In the wild, male combat and mating occurs in late winter-early spring (September), although male combat has been observed in Pseudonaja affinis tanneri in mid-spring on Boxer Island. In the mainland population male combat involves, at least partly, the combatants loosely entwining their bodies. In captivity, mating can occur year around if the temperature is kept warm enough. After mating, captive females are said to eat very large amounts of food. A captive female weighing 309g when mated weighed 580g 27 days later. This represents an 87.7 percent gain and implies a daily rate gain of about 10g per day.

Wild caught females from the mainland lay their eggs from late spring to mid-summer (mid-December to end of January). The clutch size ranges from 11 to 35 (average 21) for mainland dugites. In the smaller island Pseudonaja affinis tanneri, it ranges from 12 to 15. Eggs from mainland dugites have taken between 53 days (at 30°C) and 105 days (at 23°C) to hatch.

Conservation status

The fact that the mainland Dugite is common in degraded habitats and feeds on house mice suggests that it has a secure future.

Predators

The Dugite may fall victim to raptors, monitor lizards, feral and domestic cats, and other snakes (including its own species). Although vertebrates are probably the main predators of this snake, there is evidence to suggest that spiders occasionally snare and feed on small specimens.

Dugites are sometimes parasitized by ticks.

Danger to humans

Because of the snake’s size and highly toxic venom the Dugite is considered to be very dangerous to humans. Its prevalence in residential areas and nervous disposition have helped make it responsible for approximately 70% of all snake bites reporting to Perth hospitals, but thanks to prompt and effective intervention, there has been only one recorded fatality.

Although naturally shy, the Dugite is easily agitated when confronted and will raise its forebody upright in a tight S-shape. It hisses loudly before making a fast snappy strike at the offender, usually aiming high. Fortunately the fangs are very small and may not effectively penetrate solid shoes or heavy fabric; however anyone with a suspected bite should seek immediate medical attention.

1. If bitten call emergency services: Mobile phone: 112 Landline: 000
2. Apply pressure-immobilisation bandage over the injury and along the limb or affected area to prevent the venom from spreading throughout the body:

• Wind the bandage around the bitten arm or leg, starting from the bite.
• The bandage should not be so tight that it restricts blood flow.
• Wrap the entire limb, then apply a splint to prevent movement.
• Keep the victim as still as possible.
• Do not remove the bandage.

Seek medical attention as soon as possible.
First aid guidelines were correct at time of publication however these guidelines change over time. For up to date first aid information consult medical professionals such as St John's Ambulance.

References

Bush, B. et. al. (2007) “Reptiles and Frogs in the Bush: Southwestern Australia”, University of Western Australia Press

Cogger, H. (2000) “Reptiles and Amphibians of Australia”, Reed New Holland

Greer, A.E. (2006) “Encyclopedia of Australian Reptiles : Elapidae”, Australian Museum

Ehmann, H. (1992) “Encyclopedia of Australian Animals : Reptiles”, Australian Museum, Angus & Robertson

Mirtshin, P. and Davis, R. (1991) “Dangerous Snakes of Australia”, revised edition, Ure Smith Press

Wilson, S. and Swan, G. (2008) “A Complete Guide to Reptiles of Australia”, Reed New Holland