Acanthophis

Acanthophis is a genus of highly venomous elapid snakes. Commonly called death adders, they are native to Australia and nearby islands, and are among the most venomous snakes in the world. The name of the genus derives from the Ancient Greek acanthos/ἄκανθος "spine" and ophis/ὄφις "snake", referring to the spine on the Death adder's tail.

Seven species are listed by ITIS, though it remains unclear how many species this genus includes, with figures ranging from 4 to 15 species being quoted (see Taxonomy).

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Description

Death adders are very viper-like in appearance, having a short, robust body, triangular shaped heads and small subocular scales. They also have vertical pupils and many small scales on the top of the head. Their fangs are also longer and more mobile than for most other elapids, although still far from the size seen in some of the true vipers. Despite their name and appearance, they are not vipers at all. This is a case of convergent evolution.

It normally takes 2 – 3 years to reach adult size. Females are generally slightly larger than the males. They can also be easily distinguished from other Australian snakes because of a small, worm like lure on the end of their tail, which is used to attract prey. Most have large bands around their bodies, though the color itself is variable, depending on their locality. Colors are usually black, grey or red and yellow, but also include brown and greenish-grey.

Hunting

Unlike most snakes, Death adders do not actively hunt, but rather lie in ambush and draw their prey to them.

When hungry, Death adders bury themselves amongst the substrate. This may be leaf litter, soil or sand, depending on their environment. The only part of themselves they expose are their head and their tail, both generally very well camouflaged. On the end of the tail is a caudral lure which is placed in front of their head, and when shaken/wiggled very quickly is easily mistaken for a grub or worm. An unsuspecting bird or mammal will eventually notice the 'easy lunch' and attempt to seize it. Only then will the Death adder move, lashing out with the quickest strike of any snake in the world. A Death adder can go from a strike position, to strike and envenoming their prey, and back to strike position again, in as little as 0.13 of a second, literally in the blink of an eye.

Venom

Death adders inject on average 40 – 100 mg of extremely toxic venom (0.4 – 0.5 mg/kg murine LD50, subcutaneous) with a bite. This makes an untreated death adder bite one of the most dangerous in the world (rated in top 10 in the CSL list).

Death adder venom is completely neurotoxic, containing neither haemotoxins or myotoxins, unlike most venomous snakes.

Humans and bites

A bite from a death adder causes paralysis. While this paralysis is very minor at first, it can cause death from a complete respiratory shutdown in as little as six hours. Symptoms peak in 24 – 48 hours.

Symptoms of envenomation can be reversed through the use of death adder antivenom, or using anticholinesterases, which break the synaptic blockade by making acetylcholine more available to the parasympathetic nervous system, thus mitigating the effects of the venom.

Before antivenom was introduced, 50% of death adder bites were fatal. Now, with the antivenom, and due to the slow progression of envenomation symptoms, fatalities from death adder bites are very rare in Australia. In New Guinea, deaths from these snakes are still common.

Taxonomy

Although the Death Adders resemble vipers of the Viperidae family, they are really members of the Elapidae family, being more closely related to cobras, mambas, and coral snakes.

It remains unclear how many species this genus includes. Traditionally, only A. antarcticus, A. praelongus and A. pyrrhus have been recognized. In 1998 five new species were described (A. barnetti, A. crotalusei, A. cummingi, A. wellsei and A. woolfi)^[1] and in 2002 an additional three were described (A. groenveldi, A. macgregori and A. yuwoni).^[2] These were received with scepticism,^[3][4][5] and only A. wellsi, where an extended description has been published,^[3] has been widely recognized. Further confusion exists over the Death Adders from Papua New Guinea and Indonesia. They have variously been placed in A. antarcticus or A. praelongus. In 2005 it was shown that neither is appropriate,^[6] and the New Guinea Death Adders fall into two main clades: The rather smooth-scaled A. laevis complex (incl. Death Adders from Seram), and the rough-scaled A. rugosus complex. The latter can be divided into two sub-clades; one, A. rugosus sensu stricto, from southern New Guinea, and a second, A. hawkei, from northern Queensland and the Northern Territory in Australia. It is likely some of these include more than one species, as populations included in e.g. A. laevis show extensive variation in both pattern and scalation.^[6]

References

• The Reptilian Magazine; Volume 3, number 4, pp. 7-21 and Volume 3, number 5, pp. 27-34.