Palm Pit Vipers Of The Genus Bothriechis
Middle America—the area connecting North and South America that stretches from Mexico through Panama—is a geologically complex region. Characterized by lowlands near the coasts and mountain ranges that form a discontinuous backbone, the region supports an intricate mix of ecological zones. As one travels in elevation in the mountainous areas, temperatures begin to decrease and precipitation is often the rule. Low cloud banks hover over these elevated areas, creating frequent mist that bathes the vegetation. Epiphytes such as bromeliads and orchids flourish due to the high relative humidity, and mosses, ferns and palms are bountiful. Within this “cloud forest” habitat the view is seldom clear as the mist constantly wisps through the trees.
A number of reptile species occur in this unique realm, and possibly the most interesting are the arboreal venomous snakes known as the palm pit vipers. Nine of the 10 known pit viper species of the Bothriechis genus are adapted to these mountainous regions; areas that while considered tropical experience somewhat cooler temperatures than the surrounding lowlands. Relatively small (2 to 3 feet) and slender, palm pit vipers are often observed among low-lying palms, hence the name.
More Pit Viper Information
Without question, the eyelash viper (B. schlegelii) is the best-known palm pit viper. Named for the raised superciliary scales above each eye, the eyelash viper comes in a bewildering array of colors. Green seems to be the most common, but eyelash vipers may be tan, rust, pink, yellow or almost white in coloration. While most palm pit viper species are considered highland species, the eyelash viper is the only one that is more common in lowland habitat, ranging from Chiapas, Mexico to Tumbes, Peru. That said, it has also been recorded at elevations above 2,500 meters in Colombia. Predominately nocturnal (upland populations may be diurnal), the eyelash viper is generally found in low vegetation and branches. A variety of prey species have been recorded, including frogs, anoles, rodents, birds, bats and opossums.
Originally described over 50 years ago by University of Kansas herpetologist Edward Taylor, the Costa Rican blotched palm pit viper (B. supraciliaris) was considered a variant of the eyelash viper until it was revalidated several years ago, though it still remains under taxonomic uncertainty as of this writing. It is very similar to the eyelash viper in that it is variable in ground color, with individuals ranging from green, brown and red to yellow, and it, too, has raised superciliary scales above each eye. Slight variations in markings on the dorsum as well as scale counts are the primary differences between B. supraciliaris and B. schlegelii. Found in southwestern Costa Rica, it occurs at elevations of 800 to 1,700 meters, and it is speculated that the Costa Rican blotched palm pit viper is possibly more terrestrial than the eyelash viper.
The Merendón palm pit viper (B. thalassinus) was confused with the Guatemalan palm pit viper until just a few years ago, when it was described as a separate species. Named after the Sierra de Merendón, it occurs in montane moist and wet forest habitat at 885 to 1,730 meters in eastern Guatemala to western Honduras. Blue-green in coloration, many specimens exhibit black mottling on the dorsum, not unlike that found on the black-speckled palm pit viper that occurs further south in Costa Rica and Panama.
Possibly the rarest species of palm pit viper is found in the highlands of the Mexican states of Oaxaca and Chiapas. Rowley’s palm pit viper (B. rowleyi) was described in 1968 by American Museum of Natural History herpetologist Charles M. Bogert from a specimen found by an ornithologist the previous year in a remote region of Oaxaca. True to name, all specimens of this rarely seen green pit viper have been found in the vicinity of palm thickets, and the holotype was discovered when a hummingbird was noticed frantically flying above the stalk of a palm. Some mystery surrounds the collector, J. Stuart Rowley, who was found dead at the base of a cliff in Oaxaca the following year.
March’s palm pit viper (B. marchi) inhabits low to intermediate elevations (500 to 1,500-plus meters) in Honduras and possibly as far south as Nicaragua. Another green-to-bluish-green species, it was named after Douglas March, the head of the serpentarium in Tela, Honduras, during the 1920s. At the time, to March’s knowledge, the only green arboreal pit viper to occur in the area was the eyelash viper. The discovery of this species came after conversations with locals who described a green arboreal snake that lacked the “horns” of the eyelash viper, and which was responsible for the death of three men. Several specimens were promptly secured by March from Quimistan and La Cumbre, Honduras.
The Guatemalan palm pit viper (B. bicolor) occurs at moderate to intermediate elevations (500 to 2,000 meters) from southern Mexico to Guatemala. The Latin specific name bicolor refers to the contrasting green-to-bluish-green dorsal coloration and the snake’s yellow-green venter. The habits of this snake are not well known, though specimens have been observed as active only at night in low vegetation.
One of the more striking species, the yellow-blotched palm pit viper (B. aurifer) is predominately green in coloration with a series of yellow blotches bordered in black. Ranging from Chiapas, Mexico to Guatemala, it is found in cloud forest at moderate to intermediate elevations (1,200 to 2,300 meters). This diurnal species forages among dense vegetation and terrestrial bromeliads in Guatemala. During the past decade or two, B. aurifer, like many palm pit viper species, has become rare due to deforestation.
The species that reaches the highest elevations is the black-speckled palm pit viper (B. nigroviridis), which is known to occur at over 3,000 meters. Ranging from Costa Rica to Panama, this heavily black-mottled, green species is considered rare wherever it occurs. Predominately nocturnal, it feeds upon frogs, small rodents and birds. Similar to other species of palm pit viper, B. nigroviridis has been observed to gape when threatened.
The side-striped palm pit viper (B. lateralis) is generally found in lower montane forest (850 to 2,100 meters), but has also been recorded at elevations nearing 2,800 meters. The specific name of lateralis refers to the yellow stripe on the snake’s lower green dorsum. Ranging from Panama to Costa Rica, undocumented reports suggest it may also occur in southern Nicaragua. Frequently found near streams, this species appears able to survive to a certain extent in cultivated areas, such as coffee plantations, where it feeds upon lizards and mammals. Like several other palm pit viper species, young side-striped palm pit vipers go through an ontogenetic color change as they mature. It has been observed that the brown juveniles are found closer to the forest floor than the green adults, which are usually encountered in leafy vegetation.
In 2013, a new species of green montane pit viper was formally described from specimens collected in 2010 from the cloud forest in the Texiguat Wildlife Refuge in eastern Honduras. Named after a grass roots conservationist who was gunned down in 2007 as he was trying to set up a reserve for an indigenous group, Guifarroi’s palm pit viper was recommended for immediate critically endangered status due to its extremely limited distribution and pressures from logging and ranches.
An Imperiled Future
With the possible exception of the wide-ranging eyelash viper, most palm pit viper populations are under extreme pressure from mankind. Simple prejudice against snakes results in their senseless slaughter, but larger pressures exist. In their discussion of the future of Honduran amphibian fauna (which holds true for reptiles as well), McCranie and Wilson (2002) identified habitat alteration and destruction as the most overwhelming threat for survival. These authors note that “Honduras is rapidly becoming an overcultivated, overgrazed, and overlumbered wasteland” and chainsaws, machetes and matches are that region’s most “dangerous tools.”
In Guatemala, home to four species of palm pit viper, Campbell (2001) notes that many species of herpetofauna are drastically affected by even limited clearing in cloud forests. The yellow-blotched palm pit viper was one species identified as being particularly vulnerable to even slight alteration of virgin cloud forest. Unfortunately, much of the cloud forest in that country was cleared during the 1990s and B. aurifer has become increasingly rare (Campbell and Lamar, 2004). The Guatemalan palm pit viper is another species under extreme pressures and is “now rare at the lower elevations owing to habitat destruction” (Campbell and Lamar, 2004).
Further south in Costa Rica, habitat destruction has affected populations of both the black-speckled palm pit viper and the side-striped palm pit viper. Although the latter species seems somewhat adaptable to agricultural areas, it appears to be slowly disappearing from altered habitat (Campbell and Lamar, 2004).
Eyelash Viper Captive Care
The eyelash viper is the most commonly available species of palm pit viper. Although wild-caught imports still occur, the majority of the trade in this venomous species involves captive-born specimens. Other species of palm pit viper are also occasionally imported; however, several Middle American countries have taken the initiative and now limit exports to (almost exclusively) captive-born-and-bred snakes.
Although unique and beautiful, palm pit vipers should only be kept by very experienced keepers. These snakes are not to be taken lightly, and careful handling procedures with proper tools must always be followed. Furthermore, many state and municipal laws prohibit the keeping of venomous reptiles. Bites from these snakes can be extremely serious, and deaths have resulted from envenomation by B. aurifer, B. marchi and B. schlegelii.
The eyelash viper is an easy species to keep provided certain conditions are met. Being arboreal, a vertically oriented enclosure is a must. An average-sized adult can be comfortably kept in an enclosure the size of a 10-gallon aquarium, though larger cages offer greater thermal gradients and hiding places. A secure lid with a lock or a door with a locking mechanism is an absolute must.
Cage furniture should consist of branches for the snake to perch on as well as live plants, if possible. Plants not only offer seclusion and security, but in conjunction with a water bowl they will aid in maintaining humidity. Cypress mulch is a good substrate for this tropical forest-dwelling species, as it will help retain moisture within the enclosure. A water bowl should also be supplied.
I place pieces of clear acrylic over approximately half of the screen openings of my cages to partially restrict airflow. Misting the enclosure with water from a pump sprayer or automated misting system is a necessity, as eyelash vipers may not drink directly from a water bowl but will drink droplets of water that tend to accumulate in their coils when misted.
I find that eyelash vipers do quite well in temperatures from the mid 70s to low 80s Fahrenheit. Even though I have never witnessed an eyelash viper basking when kept at this temperature range, I still maintain a basking spot that’s in the mid 80s.
Compared to other palm pit vipers, eyelash vipers are generally good feeders in captivity, but because they are sedentary snakes they do not require frequent feeding. Because eyelash vipers are generally nocturnal, one of the first “tricks” of feeding these guys is to do so after the lights have turned off. An 18-inch pair of hemostats or forceps is generally sufficient when offering food to an eyelash viper, but the length of the feeding tool will depend on the size of the snake. Make no mistake: eyelash vipers have considerable strike ranges.
Likewise, also gauge the size of the food item to the size of the snake. I tend to feed smaller prey items such as pre-killed fuzzies and small mice to my snakes. Warm prey items before feeding; vipers have heat-sensitive pits located immediately in front of their eyes that are used to locate and capture endothermic prey. While they will eat prey that has not been warmed up, I find they accept warm food items more readily. Like most arboreal snakes, eyelash vipers will strike and hang on if they are interested in the food item being offered. If at first a snake doesn’t strike, gently tap it near the tail region to try to elicit a strike. Don’t worry if an eyelash viper doesn’t feed right away, as an occasional lull in feeding is common in this species. I have had males in particular go off feed for months at a time before starting back up again.
Breeding Eyelash Vipers
Eyelash vipers are not only easy to maintain, they are also easy to reproduce in captivity. This species has been bred year around under captive conditions with little manipulation in temperatures or lighting. Having said that, a slight drop in temperature during the cooler months may help increase reproductive success. I generally shorten my light cycle as well as decrease humidity during this cooling period.
Although eyelash vipers will reproduce if kept together throughout the year, I find it easier to maintain specimens separately (which also makes feeding easier) and introduce them at periodic intervals. Immediately before introduction, the enclosure is heavily misted with water, and copulation usually occurs intermittently in the evening, after the lights are turned off.
Gestation periods are extremely variable and may vary from as little as five months to close to a year, with an average of 150 to 180 days. Gestating females do not seem to seek out higher temperatures and sometimes prefer secluded locations while gravid. I have found that ambient cage temperatures of 77 to 82 degrees work well at this time.
Husbandry and Reproduction of Montane Species
The most commonly encountered montane species is the side-striped palm pit viper, though other species are occasionally available. As with B. schlegelii, vertically oriented enclosures are best for these partial to fully arboreal species. Basic cage interiors should also be as previously described.
The primary difference when keeping montane species as opposed to the eyelash viper are in providing the proper environmental manipulations that are necessary for the long-term maintenance of the higher-elevation species. Two excellent primers one should consider essential reading before keeping montane species of Bothriechis include both Peterson and Odum (1986) and Peterson (1992).
Although upland species of palm pit vipers can be kept at temperatures similar to that of the eyelash viper, long-term success for both maintenance and reproduction is more likely when the environment more closely approximates the parameters found in the snakes’ natural habitat. Many palm pit viper species occur in areas that experience considerable seasonal fluctuations in both temperature and humidity. For example, the Pacific slope experiences a wet “warm” season from April to December and a dry “cool” season from December to April.
Temperature is closely tied to elevation, and the higher the elevation, the cooler the temperature. At elevations between 1,000 and 2,000 meters in Central America cloud forests, yearly average temperatures range somewhere between 59 and 68 degrees. Using this range as a guideline, a seasonal temperature cycling should be employed when keeping montane species of palm pit vipers. A thermal cline within the enclosure should also be utilized, with a basking area that provides warmth and a cooler area that will allow specimens to thermoregulate as needed.
Keeping humidity relatively high (above 70 percent) during the warmer season and low (below 50 percent) during the cooler period is standard protocol when maintaining montane palm pit vipers. In providing humidity cycling, a cool mist humidifier comes in handy when set on a timer. Another way to alter humidity within an enclosure is by drip watering. The basic premise is to attempt to copy the seasonal cycles these arboreal snakes experience in the wild.
As with the eyelash viper, gestation is variable in the montane forms but generally averages five to six months. Basking sites should be provided to allow females the opportunity to thermoregulate as needed.
Care and Feeding of Young Vipers
Neonates need to be set up in individual containers from the very start, as cannibalism has been noted in several species of palm pit vipers. Wide-mouth gallon jars are an easy way to house neonates, but almost any secure container will do. As neonates are prone to dehydration, add water to the bottom of the container, at least for the first few weeks of the neonates’ life. A small twig or branch will complete the enclosure. Keep the interiors as simplistic as possible, especially because young palm pit vipers can be difficult to feed and frequently will drop food items.
Feeding neonate palm pit vipers of any species can be frustrating. Not only are they small, but they will frequently refuse to strike at prey items being offered, or they don’t hang on to the food after a strike. Because of their size, extremely small items have to be supplied. This might mean offering assorted pink mouse body parts via forceps. Lightly tapping the lower half of a neonate’s body is usually effective in inducing a striking response. A quick release of the food item from the forceps is also necessary after the strike. Patience and persistence are needed during neonate feeding trials.
Although it is usually not desirable to feed wild-caught prey, it is sometimes necessary when all other methods have failed. Juvenile palm pit vipers will accept a variety of small frog and lizard species, such as Acris, Pseudoacris, Hyla, Hemidactylus and Anolis species. An interesting behavior observed in juveniles of several species is caudal luring. Loosely defined as the wriggling of the distal portion of a conspicuously colored tail in order to attract prey, it has been reported in the eyelash viper, side-striped palm pit viper and the Guatemalan palm pit viper. The waving or wriggling of the tail has been suggested by some to mimic a worm or similar invertebrate in order to attract a prey item such as a lizard or frog within striking distance.
I vividly recall the first time I saw an eyelash viper in the wild. Delicately hanging onto a vine on the side of a tree, it was an awe-inspiring sight. I was immediately hooked on these arboreal serpents, eventually acquiring captive-born stock of my own, as well as other species of palm pit vipers. Maybe someday you, too, will find yourself traveling in the tropics when you have the opportunity to observe these magnificent serpents. It would be an experience you’ll never forget.
R. Michael Burger has been involved with amphibians and reptiles for over four decades. His articles have appeared in North American and European publications, including Zoo Biology, Herpetological Journal, Herpetological Review, The Vivarium, REPTILES magazine, and in the book, Biology of the Boas and Pythons.
- Campbell, J. A. (2001). “The herpetofauna of the mesic upland forests of the Sierra Madre de las Minas and Montañas del Mico of Guatemala.” Pp. 80-92. In: J. D. Johnson, R. G. Webb and O. A. Flores-Villela (eds.) Mesoamerican Herpetology: Systematics, Zoogeography, and Conservation. The University of Texas at El Paso.
- Campbell, J. A. and W. W.Lamar (2004). The Venomous Reptiles of the Western Hemisphere. Cornell University Press.
- McCranie, J. R. and L. D. Wilson (2002). The Amphibians of Honduras. SSAR.
- Peterson, K. H. (1992). “Reproduction of the Yellow-lined Palm Viper, Bothriechis lateralis.” Pp. 65-69. In: P. D. Strimple and J. L. Strimple (eds.) Contributions in Herpetology. Greater Cincinnati Herpetological Society.
- Peterson, K. H. and R. A. Odum (1986). “Reproduction and notes on the maintenance of arboreal and terrestrial, montane Bothrops at Houston Zoological Gardens.” Pp. 187-97. In: S. McKeown, F. Caporaso, and K. H. Peterson (eds.). Ninth International Herpetological Symposium on Captive Propagation & Husbandry. Zoological Consortium.