| 1 | King cobra |
Unlike many on this list, the world’s longest venomous snake (max 4.5 metres) isn’t an arboreal or tree-dwelling snake. They primarily stick to the ground, in rainforests and evergreen forests receiving over 1500mm of precipitation annually. Yet there’s legions of stories of people accidentally finding king cobras coiled inside hollow trees. Thai villagers and European naturalists alike have peered in to find the brutish face of a king cobra staring back at them.
King cobras are so large that they’re almost an apex predator. It’s unlikely that they enter tree trunks to dodge swooping hawks – thermoregulation is more likely. There’s a very real possibility of exploring a Thai forest to search for monkeys, only for a semi-basilisk to explode out of a tree trunk towards you. If any snake could solidify the old superstition “the forest came alive and took him”, it’s the king cobra.
Luckily, they’re not quite strong enough to seize somebody by the neck and drag them back into the trunk, never to be seen again. If a king cobra is sheltering, it’s almost certainly more likely to be in a relaxed rather than aggressive state. Still, be cautious – even trees can be your enemy in an Indian or Thai forest.
| 2 | Panama dwarf boa |
Panama is a place where you can step past red-tailed coral snakes, slowly back off from hissing fer-de-lances, and congratulate yourself on your snake senses, only to look up and see a pair of yellow eyes staring at you from a tree trunk. The reason is the Panama dwarf boa, a rarely sighted species measuring 40cm.
Panama dwarf boas are non-venomous and exclusively inhabit deep forest areas. You must climb over forested ridge and through twisted jungle to find them, and even then, they’re likely to be hidden inside a hollow tree trunk. Even scientists struggle to find Panama dwarf boas; one survey of Costa Rica’s Barra del Colorado Wildlife Refuge found just 10 individuals over 8 years.
This is an immobile snake, moving cautiously rather than dashing manically after lizards. There’s a very real chance that your torch beam could reflect a pair of cunning eyes, seemingly part of the tree itself, staring into your face. This could be the end of your expedition, as you dash back to your car. Panama dwarf boas inhabit only Costa Rica and northwest Panama, and also appear in remote banana plantations and rural buildings.
| 3 | Marbled tree snake |
A harmless species of southern Africa, including Mozambique and Zimbabwe. The marbled tree boa can slither into large crevices in tree trunks created by arms splitting and crashing to the ground, but also tiny holes, that grant them access to chambers within. Snakes can access places humans couldn’t dream of, weaving through entrances of just 5cm. From the outside, it may be difficult to tell that a tree trunk hollow is even there.
As a small, 60cm snake, Dipsadoboa aulica must be concerned with their security. While no specific predators are confirmed, Africa is home to roaming ophiophagous (snake-eating) birds such as the brown snake eagle. Marbled tree boas can position themselves between overlapping branches, or always stick to overgrown thickets – both increase their chances of survival. But there’s nothing more secure than a tree trunk sanctuary where a bird literally cannot fit through the entrance, no matter how much they flap and squawk.
Dipsadoboa aulica is a mildly venomous species, but incapable of killing human beings. There’s nothing to fear if you put your hand into a tree trunk and feel scales brushing against you, perhaps while searching for fossilised insects in amber tree sap.
| 4 | Aesculapian snake |
Aesculapian snakes inhabit Italy, where they’re the most likely snake to be found in a dark, gloomy forest. They’re also the most likely snake to identify a small hole, wriggle in, and rest in a secure sanctuary inside the trunk.
Just as they’re found on tree limbs, Aesculapian snakes are found inside those trees. In the gnarliest, most twisted Italian woods near historic Rome, any tree could potentially contain one. Aesculapian snakes are fairly slow, steady snakes which constrict their mainly mammal prey. They reach a record of 225cm (average 140-160cm), and are no threat to humans. The one possible exception is triggering a heart attack, as you’re enjoying a picnic lunch and a snake slithers out of a tree.
As usual, the precise cause of Aesculapian snakes stashing themselves in tree trunks is undetermined. Shelter against predators is possible, or perhaps they enter to ambush a sleeping mammal family, before coiling up to rest. Aesculapian snakes also inhabit the Balkans and have pockets in southern Germany, in unusually warm wooded river valleys. Then there’s small invasive populations in Wales and London’s Regent’s Canal.
| 5 | Black-necked spitting cobra |
One of central Africa’s most widespread snakes, especially in Nigeria and Ghana. Black-necked spitting cobras have a cytotoxic bite, but more infamously, the power to spit 9.75mg venom globules into people’s eyes, and blind them for 3 days. This globule could come from overgrown grass, a bush, or more disturbingly, a tree trunk.
Many Nigerian locals have mentioned the tendency of this snake to hide in hollow trees, as well as termite mounds. This makes peering into a hole in a Nigerian tree a very risky business. Your face could get bitten, or a blob of venom could fly out. Theoretically, a globule could strike you as you walk past, although since they aim for the eyes, this would be more likely to strike you on the side of the head.
Black-necked spitting cobras measure up to 200cm, but are relatively thin, allowing them to weave through small gaps, and coil up cosily inside a tree trunk sanctuary. They rely on venom rather than crushing constriction, and have no need for thickness. Black-necked spitting cobras are fast-moving and easy to recognize via their flared hood, and blacker appearance than the nearby forest cobra. Though agonising, victims’ eyes usually heal and regain their vision several days post spray.
| 6 | Horseshoe whipsnake |
This Spanish snake’s tendency to stash itself in tree trunks has had grave consequences. Horseshoe whipsnakes are extremely common in Spain, and can prey on anything, and occupy various habitats. Olive plantations are a popular haven for this snake, where they often slither up and thread into narrow crevices in bark. There they rest unbeknownst to the workers harvesting the valuable olives above their heads.
Many people have walked past this snake while stashed inside a tree trunk, mostly harmlessly, as horseshoe whipsnakes are completely non-venomous. The one grave consequence has been the invasion of Iberia and Mallorca, and the decimation of the native wall lizards there. 2 decades ago, there was a huge trend for ornamental olive trees planted in gardens. These were uprooted from mainland plantations and transported across the sea, allowing horseshoe whipsnakes to slither out and conquer an all new island.
The problem is that Ibiza and Mallorca have no native snakes, and the poor wall lizards have no defensive instincts against them. Either way, if an olive tree starts hissing at you, you haven’t lost the last tattered shreds of your sanity. Ladder snakes are another Spanish species to stash themselves in tree trunks.
| 7 | Eastern bark snake |
The eastern bark snake is an African species measuring 30-40cm, which is most abundant in Zimbabwe. They live on tree branches, and their speciality is their excellent camouflage. They have a mixture of brown and grey shades, to perfectly blend with a tree’s bark and wood. However, they sometimes take it to the next level, and rather than mimicking the tree, they enter the tree.
To a human, the entrance looks like a miniature knoll in the tree. It looks like nothing, but to a snake, it’s the equivalent of a human walking up to a small cave. To a snake, it’s actually the entrance to a sanctuary of bark and maybe ants crawling past, where they have total security from Africa’s harsh landscapes.
Do these tree hollows have any dangers for snakes? Perhaps getting stuck in amber sap, later to become a fossil experimented on by a well-meaning but clearly mad scientist. Or perhaps getting overrun by an ant swarm and devoured. The tree could also be blown over and land in a river, drowning the snake. But even most land snakes are competent swimmers, and the eastern bark snake could slither free, disappointed that its den is ruined, but alive and unharmed. Eastern bark snakes have a mild venom, but cause very few bites, partly because they spend so much time in trees.
| 8 | Red-tailed green ratsnake |
A Malaysian and Indonesian snake which lives on branches and has an infamously blue tongue. They also have blue skin on their chest, visible when they inflate themselves to warn potential predators.
Red-tailed green ratsnakes (Gonyosoma oxycephalum) can be seen resting calmly on tree branches, or threading along a branch to investigate a scent trail. They’re sensitive to any subtle movement in the forest, any bird scent which was formerly distant but now intensifying. Red-tailed green ratsnakes hunt by day, and use their extremely strong eyesight to lunge at birds or bats flapping past. When the sun sets, they retreat to the security of hollowed out chambers within the trunk of the tree they’re balanced on.
They coil up, and with nothing but sap and bark and woodlice for company, they ponder the day’s activity. They run through datastreams concerning the pathways of nearby birds and the typical distance of failed strikes. They consider the energy levels of the local bats and whether they too should act more aggressively. They decide whether to stick to their current location, or seek out a more bountiful forest corner.
The red-tailed green ratsnake then falls asleep, to regain its energy before the next day’s hunting. Tree trunk chambers are a fully secure place from hawks and eagles, and as a tree branch dweller, this species is more vulnerable than most.
| 9 | Annulated cat-eyed snake |
This South American species takes hiding in tree trunks to an industrial level. The annulated cat-eyed snake (Leptodeira annulata) is a mildly venomous species which spends 95% of its life on branches, hunting for tree frogs and their eggs. They’re nocturnal, resting during the day inside the best shelter available to them: small chambers within gnarly tree trunks.
A study from southwest Brazil’s Pantanal wetlands found that they specifically emerged at 18:30, poking their heads out to scan their surroundings. This is a fast, agile snake, and species they coexist with include Brazilian smooth snakes and yellow-bellied liophis, which prever rivers and rivershores. If there’s any snake where you can sit on your jacket on the grass, waiting for the snake to emerge at sunset, it’s Leptodeira annulata. With camera in hand, maybe an artist’s sketch pad, the hours would whittle away, all the while knowing that cat-eyed snakes were in a nearby tree. Then the moment of truth happens, and a face pokes out, slowly followed by a body.
Capturing a Leptodeira annulata emerging from its tree would be an epic task on par with filming a bear emerging from its hibernation den following winter. The problem would be selecting the actual tree. At 18:30, your eyes might be fixed on the tree in front of you, while an unnoticed cat-eyed snake pokes its head out of the tree behind you. Luckily, this is an abundant snake, and many can live in one area.
| 10 | Stephen’s banded snake |
Being a lumberjack is a risky job, what with all the falling tree trunks. Usually, once the timber is safely stacked, the risk decreases, but Australia is the land where you can hear a piercing hiss as a sudden snake bursts out the pile the moment you let your guard down.
Stephen’s banded snake (Hoplocephalus stephensii) is a species of Australia’s populous east coast, which is moderately venomous and has caused one confirmed death. They measure up to 120cm, and shun open arid areas. Instead, they appear anywhere trees grow, from isolated clumps to fully fledged forests. Stephen’s banded snakes appear anywhere on trees: at their foot, 15 metres high, on a mid-height branch, or nestled within secret sanctuaries inside the thick tree trunk. They like to stash themselves when not hunting, accessing by tiny entrances.
Carve up some timber and there’s a great chance of cutting into these sanctuaries, revealing the hidden snake inside. They could also crawl out while the logs are being transported on trunks, spooking the driver, causing a pile up which only the snake slithers away from unconcerned.