There are many misconceptions about Australian snakes that can lead to potentially dangerous misidentifications.
- Twenty venomous species have been documented climbing trees, and many more engage in climbing when under stress
- The number of venomous climbing snakes is likely much higher than what this study captures
- Historical migration routes help explain why many non-venomous snakes in Australia are climbers
A myth that still pops up from time to time is that most poisonous snakes don’t climb – that is. if you see a snake in a tree or on a roof, it is either a harmless tree snake or a python.
But a study by three snake experts definitively dismissed that idea.
Their research, published in Herpetology Notes late last year found cases of escalation in a wide range of venomous (elapid) Australian snakes, including royal browns (Pseudechis australis), tiger snakes (Notechis scutatus) and the spectacularly patterned Collett’s snake (Pseudechis colletti).
In total, their research, based on studies of the literature, surveys and personal observations, found cases of 20 different species of poisonous snakes engaging in arboreal behavior – climbing trees.
When their observations were expanded to include venomous snakes climbing things other than trees, or snakes under extreme stress, such as when fleeing from predators or ascending flood waters, the number of climbing species rose. at 31.
“Even though we have 31 species recorded, which is just over a quarter of all [Australian] stoned, that number is likely to be higher,” said Matt Sleeth, ecologist and lead author of the paper.
“Due to the difficulty of investigating this behavior in these animals, it is likely that there are more [venomous elapid] climbing snakes.”
A grain of truth?
So where does the misconception come from?
Like most rumors, it is based on some truth.
In Australia, there are five families of land snakes: pythons, bloodhounds, blind snakes, rear-toothed or colubrid snakes, and front-toothed or elapid snakes.
Blind snakes are small, shy, and rarely seen, lime snakes are aquatic and live in northern swamps and billabongs, and pythons are widespread, non-venomous, and prolific climbers.
Then there are the other two: elapids and colubrids.
Almost all of our poisonous snakes belong to the Elapidae family.
Globally, elapids include Asian and African cobras, African mambas, as well as coral snakes, sea snakes and, in Australia, over 130 species of land and sea snakes.
While many elapids have developed venom, the elapids of Australia are singular in their potency. The most venomous land snake in the world, the inland taipan, is capable of killing around 250,000 mice with the venom of a single bite, according to the LD50 parameter.
Elapids are thought to have arrived in Australia millions of years ago as a sea serpent, according to evolutionary ecologist Rick Shine of the University of Sydney.
“In the case of elapids, the ancestor that came from Asia to Australia appears to belong to a modern-day krait – a species of sea serpent,” Professor Shine said.
Today, sea kraits are among the most venomous snakes in the world, which means Australian elapids probably had a head start in their development of potent venom.
It also means that the elapids of Australia started out as land snakes.
Although some settled in the trees, Australia then underwent a process of aridification – much of the vast forest that once covered the continent turned into deserts and grasslands.
If any of these early Australian elapids had moved into the trees, Australia’s aridification would have worked against them, according to Matt Sleeth.
“Compared to places like Asia and Africa where there is a lot of forest habitat, Australia is much drier, so the potential for [tree dwelling] to be beneficial is limited,” he said.
Selection for non-venomous climbers
Which brings us to colubrids or rear-toothed snakes like the common tree snake, brown tree snake, and keelback.
Colubrids are the most successful family of snakes in the world, and Australia is unique in that it is the only continent where elapids outnumber colubrids – only 10 species of colubrids occur here, according to Queensland Museum.
Colubrids are thought to have arrived in Australia after the elapids, but there is still some debate as to when exactly.
And the path they took to get here probably explains why many Australian colubrids are tree specialists.
This means that their migration path was heavily forested and favored arboreal species.
“There’s probably a link there where you’re likely to get more tree species,” Professor Shine said.
This migration route is the likely explanation for why many of Australia’s nonvenomous colubrids are climbers.
Combined with the presence of non-venomous pythons, which also tend to climb, it is easy to see where the myth that climbing snakes are not venomous comes from.
But even though it’s a trend, it shouldn’t be confused with a rule, according to Matt Sleeth.
“Myths among the public are quite prevalent, especially among non-charismatic species like snakes,” he said.
“As a rule of thumb, if you see a snake in a tree, it’s likely to be a non-venomous python or a tree snake…but it doesn’t have to be.”
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