| 1 | Eyelash viper |
Maximum length: 91.6cm.
Central America is a paradise of pitvipers, with dozens upon dozens of species, each divided neatly into separate habitats to avoid competition with each other. The local rattlesnakes prefer relatively dry areas, while hognose pitvipers (Porthidium genus) stick to leafy rainforest floors.
The Bothriechis genus, meanwhile, has claimed the niche of tree branches within rainforests. This venomous group ranges from southern Mexico to Ecuador, and is usually green, but very small, with even the largest members rarely exceeding 1 metre.
Of the 19 Bothreichis members, the most common is easily the Central American eyelash viper (Bothriechis nigroadspersus), which is abundant in Costa Rica, Panama, Honduras, Nicaragua and Guatemala. This is a venomous snake averaging at 40-80cm, which has an extreme variety in appearance – they can be banana yellow, mossy grey, or even “Christmas” green-red, even within one location.
Central American eyelash vipers typically rest on branches at chest height or above, causing them to strike the chest or arms. Their bites lack neurotoxins and are rarely fatal, but can cause swelling and haemorrhaging, or necrosis and lasting deformities in unlucky cases. Haemorrhagic blood blisters are one particularly nasty effect.
Eyelash vipers are also myotoxic, i.e. they attack muscle tissue. In a study on 10 Costa Rican pitvipers, eyelash viper venom ranked first for myotoxicity alongside the infamous fer-de-lance. Luckily, the venom yield is low, at 10-20mg versus 400-500mg for the fer-de-lance (Cenrtal America’s deadliest snake).
| 2 | Black-speckled palm pitviper |
Maximum length: 93.7cm.
One of the deadlier members of the Bothriechis pitviper clan. The black-speckled palm pitviper (Bothriechis nigroviridis) is an abundant species in Costa Rica, as well as far western Panama. This species also clings to branches at around eye height, but prefers higher altitudes to the eyelash viper. Instead of lowland rainforests, this species inhabits mountain ranges at altitudes of 1150 to 3000 metres, including Costa Rica’s Tilarán and Talamanca Cordillera ranges.
The black-speckled palm pitviper measures up to 93.7cm, and has a highly separate venom profile to the eyelash viper. Its venom produces no haemorrhaging, only minor swelling and coagulant effects, and has moderate myotoxic (muscle-assaulting) properties. However, it’s still more lethal than the eyelash viper overall.
The reason is a rare neurotoxin called nigroviriditoxin, first discovered in 2015. This single toxin makes the black-speckled palm pitviper much more likely to cause paralysis and laboured breathing than its cousins. The further north you travel in Costa Rica, the more this neurotoxin increases, with one extreme venom sample containing 60.3% nigroviriditoxin.
Luckily, an antivenom raised against the South American rattlesnake (another neurotoxic species) managed to neutralise the lethal effects of this species as well. That said, the black-speckled palm pitviper lives in such remote mountains that reaching hospital in time may not be possible.
| 3 | Side-striped palm pitviper |
Maximum length: 95cm.
The second most widespread member of the Bothriechis pitviper genus. Side-striped palm pitvipers (Bothriechis lateralis) inhabit most of central Costa Rica, especially the north, and also western Panama. They prefer humid rainforests at moderate altitudes, usually between 850 and 2100 metres.
Compared to the common eyelash viper, this species is nearly always green, with little colour variation. There’s also a thin white (or yellow) stripe on each flank, which eyelash vipers completely lack.
Instead of neurotoxic effects, the side-striped palm pitviper is more likely to trigger haemorrhaging. Its venom consists of 55% snake venom metalloproteinases (SVMPs), which degrade type 4 collagen in blood vessels and cause them to rupture.
Luckily, this venom seems relatively easy to cure. There’s no dedicated antivenom, but an antivenom designed against the notorious fer-de-lance was highly effective, as was one designed against the Central American rattlesnake. Statistics are hard to come by, but a 1984 report mentioned 41 bites per year in Costa Rica, with no deaths, but often permanent injuries to the hands.
While Bothriechis lateralis spends most of its life on branches, females descend to the ground to give birth (as live young). These newborns measure 19.6 to 25.5cm, while adults measure up to 95cm. Younglings prey on leaf litter anoles and Eleutherodactylus frogs, while adults graduate to rodents and even bats.
| 4 | Guifarro’s palm pitviper |
Maximum length: 76.5cm (so far).
A lot of newly discovered snakes are secretive burrowers, which you can easily understand people missing for hundreds of years. But new pitvipers are occasionally found as well, and one was Bothriechis guifarroi in 2010.
This species is found only in the fragmented cloud forests of northern Honduras, specifically in the Texiguat Wildlife Refuge. This sanctuary was created in 1987, primarily to protect endangered white-faced monkeys, howler monkeys and jaguars, but also any undiscovered creatures that could be hiding, whether in the towering tree canopies or bushy undergrowth below.
Like its entire genus, Bothriechis guifarroi is a branch clinger. As the image above shows, blue skin is often visible between its leafy green scales. All adults are this mainly green colour (including the eyes), but juveniles have two colour phases: one green, and one brown, which eventually converge. Meanwhile, side-striped palm pitvipers are always brown as newborns, sometimes with red patches, before gaining their standard green as an adult.
Being so new, nothing is known about Bothriechis guifarroi’s venom. The species was named after Mario Guifarro, a gold miner who became a conservationist after watching huge swathes of rainforest being slashed down and converted to cattle ranches. He aimed to secure a parcel of untouched land for the native Tawahka people, to the anger of shadowy businessmen. Guifarro avoided multiple attempts on his life, but was finally ambushed and killed on September 15th 2007.
| 5 | March’s palm pitviper |
Maximum length: 104cm.
This species lives in one poorly studied region of northwest Honduras, mainly at high altitude forests above 1500 metres. March’s palm pitviper (Bothriechis marchi) reaches a maximum of just over 1 metre, and preys on mammals like Mexican deer mice, and amphibians such as Honduras spikethumb frogs.
Bothriechis marchi is an interesting snake. They have a very small range, mainly inhabiting the Sierra de Omoa mountains on the border with Guatemala. At first glance, it seems like they’re barely clinging onto existence. Yet within hotspots like Cusoco National Park, they’re extremely abundant. At 176 sightings, a 13 year survey found that they were the second most common pitviper inside after Wilson’s montane pitviper (513). They were far more common than the widespread eyelash viper (5) and fer-de-lance (5).
March’s palm pitvipers are fully arboreal and rarely stray to the ground. Dense closed canopy forests are their heartlands, typically close to a stream.
This seems to be one of the highest climbing Bothriechis members, as a 2022 study found that their average perch height when tracked by radiotransmittor was 17.04 metres above ground. The average temperature of observations was 15C, relatively cool. One of the March’s palm pitvipers the scientists tracked stayed completely still for several weeks.
Like all Bothriechis members, this is a committed ambush hunter. Another special feature is a fluorescent tail tip they use to lure in curious prey.
| 6 | Yellow-blotched palm pitviper |
Maximum length: 100cm.
This venomous branch snake mainly inhabits central and northwestern Guatemala, as well as a tiny portion of Chiapas, Mexico just over the border. Like March’s palm pitviper, it has a narrow range, yet is abundant in certain spots, particularly in the hills surrounding the Guatemalan town of Tactic.
The yellow-blotched palm pitviper (Bothriechis aurifer) is one of the more recognisable members, as there’s nearly always a thick black marking extending from each eye. They’re nearly always green, and then there’s a spinal pattern consisting of broken yellow blotches with a black outline, which is found in over 50% of individuals (see here).
Its venom was studied in 2017, and revealed to consist of 33-39% metalloproteinases, with a helping of CRISP toxins and bradykinin-potentiating peptides. This is closer to the eyelash viper and B. lateralis, shunning the lethal neurotoxic profile of the black-speckled palm pitviper. Bite reports are few, but with this toxin makeup, swelling and moderate haemorrhaging is most likely.
Yellow-blotched palm pitvipers live at 1200-2300 metres above sea level, though a few strays have appeared lower down. Their habitats are the same as most Bothriechis: moist forests with a closed canopy, preferably near a stream. Don’t search for this species in a desert or on a grassy hillside; you’ll probably just stumble into a rattlesnake’s lair instead.
| 7 | Guatemala palm pitviper |
Maximum length: 100cm.
A palm pitviper species with virtually no research to its name. Similarly to Bothriechis aurifer, this species straddles the border between Guatemala and Mexico, but lives much further south, and has no overlap. Guatemalan palm pitvipers (Bothriechis bicolor) appear in foothills between 900 and 2090 metres in elevation, and adults are green with occasional blue speckles. Sometimes the blue is missing, but in others, the blue patches become fully fledged neon stripes (see here). A handful even have sapphire blue eyes.
There isn’t a single detailed bite report for this pitviper, although local Guatemalan villagers have doubtlessly been bitten without realising how rare this species is. What we know so far is that its venom differs from the nearby March’s palm pitviper and Bothriechis aurifer.
Firstly, Guatemalan palm pitvipers have far fewer metalloproteinases than other Bothriechis members. Secondly, 35.2% of their venom consisted of PLA2s, which is far higher than in Bothriechis aurifer, which contains virtually none. We still don’t know the exact implications, as PLA2s are very diverse, and can act as haemotoxins, myotoxins and neurotoxins alike.
Either way, a smart traveller would stay well away from this species’ lairs. Bothriechis bicolor relies on the usual ambush tactics, and is most commonly observed at 2-3 metres above ground on a branch.
| 8 | Blotched palm pitviper |
Maximum length: 58.3.cm.
A relatively rare Bothrechis member, which appears only in southeastern Costa Rica and extreme western Panama. The blotched palm pitviper (Bothriechis supraciliaris) appears at higher elevations than the neighbouring eyelash viper, usually at 800-1700 metres. While still a branch dweller, they spend more time on the ground than other members.
This species is particularly short, maxing out at just 58.3cm. However, they possess the advantage of flexibility. Blotched palm pitvipers appear in dense forests with closed canopies, but also in regenerating forests damaged by mankind, and even on the edges of farm fields, if there’s sufficient vegetation.
Blotched palm pitvipers are similar in appearance to their eyelash viper neighbour, as both possess the elevated mini horns above each eye. There’s a few differences though, as in blotched palm pitvipers, the bodily markings are more clearly defined, with less messy patterns inbetween. Blotched palm pitvipers can be jungle green, but also have a common morph which is minty green, overlaid with brown markings.
A venom analysis from 2012 revealed weak pro-coagulant activity, moderate myotoxicity, and strong haemorrhaging properties, with no mention of neurotoxins. The venom was relatively non-lethal, and easily neutralised by a standard viper antivenom.
| 9 | Rowley’s palm pitviper |
Maximum length: 97.3cm.
Also known as the blue-tailed palm pitviper. Rowley’s palm pitviper (Bothriechis rowleyi) is a high altitude pitviper, ranging from 1096 to 1830 metres, and rarely encountering local villagers.
This is another ultra rare species, known from just a few localities in Chiapas and Oaxaca states, extreme southeast Mexico. Its territory is shrinking all the time, with its native cloud forests being pushed back steadily by the march of deforestation. Rowley’s palm pitvipers can’t stand meadows, rocky hillsides, and farmland, and an urban town would be about as appealing as Mordor to them. Dense, untouched forests are their only sanctuary.
With its occasional blue patches, this species looks similar to the Guatemalan palm pitviper a few hundred miles away. But there’s one easy ID sign with Bothriechis rowleyi: yellow eyes rather than green.
This species was discovered by J. S. Rowley, who died just a few months after its discovery, when he fell off a cliff in Sierra de Cuatro Venados (also Oaxaca state). The original Rowley’s palm pitviper was discovered after a hummingbird was spotted flying frantically near some palm thickets, perhaps in a desperate escape attempt. Virtually nothing is known about this species’ venom, apart from vague assumptions.
| 10 | Talamancan palm pitviper |
Maximum length: 93.7cm.
The rarest Bothriechis pitviper in Costa Rica. To find this venomous forest dweller, you must hike deep into the Talamanca Cordillera on the border with Panama, a pristine realm of tiny farming communities and obscure hiking trails.
This species was only made official in 2016. The first specimen was discovered in 2001, but was so similar to the black-speckled palm pitviper that it was assumed to be the same species. According to the initial discovery, the Talamancan palm pitviper (Bothriechis nubestris) inhabits the transition zone between cloud forest and montane rainforest, and had only been found at between 2400 and 3000 metres. The Latin title nubestris translates as “belonging to the clouds”.
Talamancan palm pitvipers share the neurotoxic nigroviriditoxin of their cousin, but in far smaller percentages: 0.7% versus up to 60.3%. Instead, this has a more typical Bothriechis venom, specialising in haemorrhaging, with snake venom metalloproteinases (SVMPs) contributing the most toxins at 34.9%. There’s also a PLA2 making up 15.7%, which structurally resembles a known myotoxin (muscle-assaulting toxin) in eyelash viper venom.
Together, Bothriechis nubestris and B. nigroviridis are believed to have diverged from the other Bothriechis members 7.5-13 million years ago. They then separated from each other approximately 6-10 MYA, barely changing in appearance, but diverging in their venom. Somehow, B. nigroviridis accumulated a war chest of neurotoxins after diverging, while the Talamancan palm pitviper didn’t bother.
Meanwhile, the common ancestor of the entire Bothriechis genus apparently appeared 18 MYA. Eyelash vipers (B. nigroadspersus) and blotched palm pitvipers (B. supracillis) split from the pack the earliest, diverging well over 10 million years ago.