Death adder
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The death adders are a group of three species of snakes native to the Australian continent. They are some of the most dangerous snakes in the world.
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Appearance
Death adders are very viperlike in appearance, having triangular shaped heads and subocular scales. The also have vertical pupils and many small scales on the top of the head. Like vipers, they have short, fat bodies (normally 50 – 90 cm (20 – 36 inches) long). Their fangs are also longer and more mobile than other elapids, although still far from the true vipers. Despite their name and appearance, they are not vipers at all but Elapids (like all Australian venomous snakes). 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 short spine protruding from their tails. Most have large bands around their bodies, though the color itself is variable. Colors are usually grey or red, but also include brown, greenish-grey, or yellow.
Habitat
Death adders can be found throughout the entire continent of Australia, except for Tasmania and the other southern islands. They are widespread in their preferred habitats. These habitats vary widely, but are basically undisturbed brushlands with some kind of thick ground cover. This cover could be leaves, rocks, thick grass, or almost anything else.
Death adders don't deal very well with humans, so any place that has been disturbed by civilization will likely not have them in it, although incidental disturbances, like roads, do not affect them so much. Because of this, and because of their habits, encounters with humans are uncommon.
Habits and hunting
Death adders are ambush hunters, concealing their bodies under thick cover, with only their heads and tails showing. Along with superb camouflage, this renders them nearly invisible to both predator and prey alike. At rest, they lie in a loose horseshoe shape, having the tail in front of the head.
Death adders normally hunt and rest by day and travel at night. They especially travel in unstable weather, when a storm is approaching.
Death adders often wave their tails in order to lure prey near to them. When a potential victim comes close enough, they will strike with lightning speed and nearly perfect accuracy. Fast enough that one is even able to strike an object in the air before it even touches the ground. (see Head Retraction as a Defence and Other Habits of Death Adders (http://www.smuggled.com/AddHea1.htm))
Properties of venom
Death adders inject 70 – 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.
Death adder venom is neurotoxic. It blocks the post-synaptic neuromuscular transmission from the acetylcholine receptor. Unlike other snakes of its type, it does not contain either procoagulants or myolysins., making treatment easier.
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 brain.
Before antivenom was introduced, 50% of death adder bites were fatal. Now, with the antivenom, and due to the slow progression of envenomation symptoms, deaths from death adder bites are very rare.
Taxonomy
Although the death adder appears to be a viper, of the Viperidae family, it is really a member of the Elapidae family, being more closely related to cobras, mambas, and coral snakes.
Three major species of death adders (genus Acanthophis) are now accepted in the scientific community:
- Death Adder or Common Death Adder — Acanthophis antarcticus
- Northern Death Adder — Acanthophis praelongus
- Desert Death Adder — Acanthophis pyrrhus
In addition, the status of at least two other species is currently being debated:
- Barkly Tableland Death Adder — Acanthophis hawkei
- Black-headed Death Adder — Acanthophis wellsei
The word Acanthophis means Spine snake, referring to the spine on the Death adder's tail.
References
- The Reptilian Magazine; Volume 3, number 4, pp. 7-21 and Volume 3, number 5, pp. 27-34.
- Kingsnake.com, toxinology page (http://www.kingsnake.com/)
- WCH Clinical Toxinology (http://www.toxinology.com/)