Mangrove Snakes
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By Jonathan Rheins
Mangrove snakes, Boiga dendrophila, are strikingly beautiful and notoriously aggressive colubrids locally common throughout Southeast Asia, Indonesia, and adjacent island chains. Their gorgeous color scheme and impressive attitude have captivated even the most seasoned herpeteculturist. Despite being readily available and reasonably priced, very little has been published on the natural history and captive management of these snakes in the United States.
Like many snake keepers, I have always been one to enjoy a reptilian challenge. After nearly 10 years of experience and experimentation with multiple Boiga species, it is through this channel that the results and culmination of these ventures will be shared with the herp community.
This article is by no means intended to be an authoritative or scientific work in regards to B. dendrophila or related species. The information contained herein is an in depth account of tried and proven husbandry techniques and acclimation processes used by the author and fellow hobbyists.
Nomenclature
Boiga, or cat-eyed snakes, is a genus of the family Colubridae and is comprised of more than 30 species. B. dendrophila is the species most commonly encountered in the pet trade, and is the focus of this article. Within the species dendrophilia there are between 8 and 10 recognized subspecies depending on taxonomist and publication. Some researchers have recommended elevating certain subspecies to the species level, while others feel that more sub specific delineation is warranted.
Identification of Boiga at the subspecific level can be daunting or nearly impossible without accurate data pertaining to the animal’s country of origin. Some generalizations can be made based on overall appearance and the number of yellow bands (when present), but these attributes should not be relied on for 100% accurate identification.
In the United States we are fortunate to see a handful of subspecies enter the country, and in some cases, be bred in captivity. Of these, B. d. dendrophila and B. d. melanota are the most frequently encountered, with melanota being the most common and having the wider geographic range. B. d. dendrophila is restricted to the island of Java (Brongersma, 1934), and has a naturally occurring color variation containing white bands on a black base, as opposed to the more common yellow or golden bands. It is unclear if other subspecies or geographic races can also exhibit white banding.
A third subspecies that is occasionally available is B. d. gemmicincta. Sometimes marketed as “Rainbow mangrove snakes,” these animals undergo a drastic ontogenetic color change as they mature. Neonates are often brilliantly colored with numerous, closely-spaced yellow rings that become more red at they approach the caudal region. However, by the onset of sexual maturity these individuals will lose all banding and exhibit a striking, jet-black body.
The husbandry guidelines outlined below will apply equally to any of the subspecies mentioned above, all of which I have personally worked with. Although I cannot state this with certainty, it is likely that the parameters described below will prove effective with other Boiga species as well.
Natural History
Mangrove snakes inhabit coastal lowland forests and adjacent mangrove swamps throughout their extensive tropical and sub-tropical range. They can be found near bodies of fresh or brackish water, and while primarily nocturnal, have been observed basking during daylight hours.
After dusk is when Boiga are most active. It is during this time that they actively hunt, feed, and breed. It should be noted that all of the mangrove snakes in my collection become much more defensive and easily agitated after dark. Animals that are easily worked with during the day can be nearly impossible to approach after lights out without eliciting a series of defensive strikes.
A third subspecies that is occasionally available is B. d. gemmicincta. Sometimes marketed as “Rainbow mangrove snakes,” these animals undergo a drastic ontogenetic color change as they mature. Neonates are often brilliantly colored with numerous, closely-spaced yellow rings that become more red at they approach the caudal region. However, by the onset of sexual maturity these individuals will lose all banding and exhibit a striking, jet-black body.
The husbandry guidelines outlined below will apply equally to any of the subspecies mentioned above, all of which I have personally worked with. Although I cannot state this with certainty, it is likely that the parameters described below will prove effective with other Boiga species as well.
Natural History
Mangrove snakes inhabit coastal lowland forests and adjacent mangrove swamps throughout their extensive tropical and sub-tropical range. They can be found near bodies of fresh or brackish water, and while primarily nocturnal, have been observed basking during daylight hours.
After dusk is when Boiga are most active. It is during this time that they actively hunt, feed, and breed. It should be noted that all of the mangrove snakes in my collection become much more defensive and easily agitated after dark. Animals that are easily worked with during the day can be nearly impossible to approach after lights out without eliciting a series of defensive strikes.
Venom and Envenomation
Mangrove snakes, as well as all other Boiga species, possess opisthoglyphous dentition; that is, they are rear-fanged and possess a mild venom. All rear-fanged snakes are found in the family Colubridae, and the venom of these animals varies from harmless to life-threatening. Opisthoglyphs are typically specialized feeders, and subdue prey by working it towards the back of the mouth where the specialized enlarged teeth work the venom into the prey.
Rear-fanged snakes do not have an active venom delivery system like that of pit vipers or cobras. Rather than possessing a highly developed venom gland, duct system, and hollow fangs, mangrove snakes have slightly enlarged rear maxillary teeth that must puncture the skin and allow venom to passively enter the wound. This undeveloped and inefficient delivery system makes serious human envneomations rare.
The Duvernoy’s gland is the structure responsible for the synthesis of venom among rear-fanged snakes. The gland’s secretions flow directly into the oral cavity of the snake, typically at the base of the upper posterior teeth. This function is very similar to that of human salivary glands. In fact, all snake venoms are nothing more than highly specialized digestive juices (saliva).
Some authorities feel that the Duvernoy’s gland is an evolutionary precursor to the more developed venom glands of the familiar pit vipers and cobras. Other sources indicate that the form and function of the two structures are more significantly different, and should not be considered synonymous.
The clinical effects of mangrove snake venom are poorly represented, mostly due to the low occurrence of reported envenomations outside of their native range. Furthermore, snake venom (or any natural toxin for that matter) will be tolerated differently by different people. The risk of serious allergic reaction is always a possibility with any venomous animal.
It should be noted that there are no reported cases of a human fatality occurring as a result of a mangrove snake bite. The same is true, at least in the U.S., for hospitalizations resulting from severe envenomations. Local reactions including pain, swelling, and skin discoloration have been reported, and are the possible outcomes of a serious bite from a good sized animal.
Acclimation
The vast majority of mangrove snakes offered for sale in the United States are collected overseas in their native countries, and shipped to various outlets around the globe. This is not always a negative, as some may want you to believe. Rather, it is just the necessary process for providing hobbyists with species that have proven difficult to reproduce in captivity. Without this supply of fresh bloodlines and new breeding stock, we can never hope to establish B. dendrophila in the U.S. herp trade.
With mangrove snakes, special care and attention to detail during the initial acclimation process is crucial. In my experience, I have found them to be mostly trouble free snakes once they are acclimated to captivity and to the environment provided to them. Stress and subsequent anorexia are perhaps the biggest issues to overcome when establishing wild collected reptiles. Animals that feel secure and comfortable will begin feeding sooner and will be much less susceptible to secondary issues.
Having an appropriate habitat prepared and ready to go before you obtain the animal is ideal. This will allow time to monitor temperature and humidity ranges over the course of a few days. Ensuring that all environmental parameters are within an acceptable range ahead of time will not only reduce stress for the snake, but for the keeper as well.
As outlined below, a number of appropriate and secure hiding spots must be provided to allow newly acquired snakes a range of shapes and sizes in which to conceal themselves. Feeling hidden and free of prying eyes will be crucial in allowing a mangrove snake to get used to a new situation. Frequent checking and inspection of the snake should be avoided. A quick once daily visual check of water bowl level, temps, humidity, and where the snake is spending its time should suffice.
Hydration is very important to tropical herps, especially it seems for Boiga. These animals inhabit parts of the world that are subject to extreme and nearly constant levels of monsoonal moisture and humidity. If kept in an enclosure that is too dry, rapid dehydration can occur through respiration and cutaneous water loss.
Based on personal observations, I believe that mangrove snakes are particularly susceptible to both chronic and acute dehydration. Newly acquired mangrove snakes should always have access to clean standing water, moving water multiple times a day (via misting with a spray bottle or dripper) and a 10-15 minute soak in chin-deep, warm water once every 5-7 days.
Handling should be kept to a minimum until mangrove snakes are feeding readily and regularly. Even then, the aggressive tendencies and potentially venomous bite would indicate that handling should be kept to minimum--ideally only during routine maintenance.
Housing
Mangrove snakes can be housed in any type of secure, appropriately sized enclosure. Attention should be paid to both height and floor space when selecting a habitat. These are large, active snakes that will utilize all of the space allotted to them. For this reason, only hatchling and sub-adult animals should be housed in rack units or sweater box-type enclosures.
Glass terrariums with locking screen lids are the most common cage choice; however, a large amount of heat and humidity will be lost through an open screen lid. Modification of the cage top with a piece of acrylic or other watertight material is recommended to ensure high levels of humidity are maintained within.
I use polyethylene plastic enclosures manufactured by Vision Products for all of my adult mangrove snakes. These cages are ideal for this species in many ways. They hold temperature and humidity better than any other, are easy to clean, and the opaque sides provide security for the animal. Enclosure access is through front sliding glass doors, which makes getting the animals in and out fairly simple.
Planted living vivaria are another acceptable method for housing smaller (up to 3 feet) specimens. Contrary to the popular belief that vivariums are not appropriate for snakes, I have raised a number of younger mangrove snakes in such setups. The live plants, lush landscaping, and added humidity create an ideal environment for growing Boiga. When the snake’s size becomes detrimental to the plants in the enclosure, they should be moved to a larger, more utilitarian habitat to facilitate maintenance.
Substrates
There are as many opinions about the ideal snake substrate as there are snake keepers. That said, I firmly believe that one should use what works well and what is appropriate for the species being kept. This means there is no single “best” substrate--only one that is the best for a given situation. In the case of mangrove snakes, a bedding should be selected that is easy to clean, dust-free, holds moisture, and promotes humidity.
I have been using fine to medium milled cypress mulch for my Boiga for a number of years, and have not once considered finding an alternative. Cypress mulch is naturally resistant to mold and fungus. It also holds moisture well, is aesthetically pleasing, and readily available. I whole heartily recommend using cypress for not only mangrove snakes, but for nearly all tropical herps.
During the hottest months of the year, I add a deep layer of New Zealand sphagnum moss over the top of the cypress mulch in all cages. This cuts down the rate of evaporation from my base substrate. The moss acts like a sponge, absorbing moisture when misted, and then releasing it slowly into the air over the course of the day.
Other acceptable alternatives are coconut husk beddings, either chipped or pulverized into a soil-like consistency. Orchid bark can be used as well, as can a mixture of any of the above. Time and experimentation will dictate what works best for you and your animals.
Hides and Décor
The most important thing in a mangrove snake enclosure is hides. They must feel secure and hidden to do well. A few hides of various sizes and location within the habitat are recommended. One hide on the warmer side of the cage and one in the cooler area would be the minimum. Adding additional hides at various heights within the enclosure, as well as hides of varying materials seem to work the best.
Habba hut half-logs are my hide of choice, as they are easy to clean and lift off the animals for inspection. Large cork flats and cork rounds are another great choice, and are slightly more natural looking. Snakes are not particular about their hides, as long as they are numerous and snug. Utilitarian black plastic hides also work, and are among the easiest to clean and disinfect.
A network of grapewood, vines, and artificial plants are highly recommended, especially for newly acquired mangrove snakes. These structures provide exercise and interest, but also a sort of tactile security for them when they are exploring after lights out. Keep in mind these animals are used to living in trees, bushes, and coastal mangroves. Re-creating the natural habitat as closely as possible has proven advantageous with this species, despite the typical snake-keeping formula.
Living plants should be incorporated into mangrove snake enclosures whenever possible. I have found that not only does natural look better, but the inclusion of living plants increases ambient humidity as well as providing multiple hiding opportunities. Large, hardy plants such as pothos (genus Pothos) and snake plants (genus Sansevieria) have worked well in my experience, and are easy to find. I typically rotate plants out of my enclosures every few months, as they become tattered by snake activity.
Once my current breeding pair of mangrove snakes became established and gained some size, I began to simplify their enclosures, both for my sake and for theirs. Large, angry Boiga can be incredibly stubborn about doing what you need them to, and this is only made more difficult when the last third of their body is anchored to a giant piece of grapewood! My large adults are kept on the substrates discussed earlier, and are provided with a large water bowl, at least 2 appropriately sized hides, and living plants if possible.
Mangrove snakes should be housed individually. Cannibalism is not unheard of; in fact, it is fairly common. Like most colubrids, conspecifics tolerate each other’s presence during courtship and breeding, but are best kept apart the remainder of the time. I have never observed cannibalism in action, but would hate to risk the loss of a valuable animal as a result of tempting fate.
Heat and Light
Being tropical reptiles, moderate to high temperatures should be maintained year round for Boiga. Infrared heat lamps, ceramic heat emitters, heat panels, and under tank heating pads all work well, either alone or in conjunction with each other. Heating apparatus should be localized to one end of the habitat to provide a thermal gradient, allowing the animal to choose an area that is appropriate for its current physiological needs.
An ambient air temperature between 84-880 F during the day is ideal. Temperatures can drop slightly at night, but never much below 780 F. The area directly adjacent to the primary heat source can be slightly warmer, approaching 950 F during the day and a few degrees cooler at night. I have observed my animals basking (usually after feeding) in an area over 1000 F, with a body temperature of nearly 1150 F.
Light-emitting standard heat bulbs can be used as a secondary heat source during daylight hours, but should always be shut off at night. A 24/7 daylight schedule is a sure fire way to confuse any herp and cause a myriad of secondary problems.
As with most snakes, special lighting is not required for mangrove snakes. If live plants are being used, a full spectrum florescent bulb with a low to medium UV output can be placed on a timer and set to run 12-14 hours a day. This will also provide the snake with a steady photoperiod, which is helpful during the acclimation process and during any breeding efforts.
I have maintained this species both with and without supplemental lighting. Those without light received only what ambient light entered the enclosures from the room in which they are housed. I have noticed no ill effects to the snakes or their behavior under either configuration.
Water and Humidity
As discussed in the acclimation section, keeping mangrove snakes properly hydrated is paramount to long-term health. The inclusion of a large water receptacle within each enclosure is a must. I often strive to provide water dishes that are big enough for the animal in which to comfortably soak. While I have never seen any of my Boiga soaking, this guideline still applies, as it serves as a good rule of thumb regardless. The larger surface area of a decent sized water container increases evaporation, and subsequently humidity.
Proper caging and substrate will help with maintaining adequate humidity levels. All of my enclosures are misted heavily with room temperature water twice daily. I spray each enclosure long enough to saturate the top layer of substrate, or as long as the snakes continue to drink the running water. After morning spraying, humidity levels in my Vision enclosures exceed 90%. By the time I spray again in the evening, the humidity will have dropped to around 60%. This cycle of high-to-low-to high humidity levels simulates nature, and prevents issues related to constantly warm, humid environments such as skin ailments or fungal infections.
Some of the mangrove snakes I have kept drink readily from a bowl. Others will ignore standing water completely, but will consume copious amounts of water from a pressurized misting bottle or dripper. Careful attention to the body condition of your snakes will help you determine if they are staying properly hydrated, and if any other watering methods are needed.
Feeding
Mangrove snakes are toted as be notoriously difficult to feed. This may be the case, as certain individuals or populations may have specific dietary preferences. However, before assuming that you have a stubborn feeder, ensure that all other environmental parameters are perfect. Often times simple changes to temperature, substrate, or even time of day that food is offered makes all the difference.
Always offer mangrove snakes food at night, preferably a few hours after all enclosure and ambient lights are off. This is when they are most active, and most likely to come across their meal. These animals are best fed in their enclosures until properly acclimated. The activity and stress associated with shifting them to a designated feeding container can deter them from eating entirely.
I have found many newly acquired mangrove snakes to be very shy feeders. They can become startled or intimidated by prey that is too large, too active, or the wrong color. If the specimens you are feeding were collected from the wild, consider offering them brown or black rodents as opposed to the more typical white mice, to which they are not accustomed.
In addition to color, prey size is another parameter to take into consideration. After weeks of failed feeding attempts with my first Boigas, I decided to try to replicate a bird’s nest scenario for my snakes. Being arboreal rear-fanged snakes, it seemed likely that in the wild a nest full of baby birds would be irresistible to any mangrove snake. Unable to procure an abandoned bird’s nest in a reasonable amount of time, a 16oz. deli cup was utilized instead. I placed a few field collected bird feathers and half a dozen fuzzy mice in the bottom of the deli cup. The following morning, the fuzzies were gone.
This process was repeated once a week until the snakes began to grow noticeably and have healthy, regular stools. From then on, the prey size was slowly increased each week, but only less active non-weaned rodents were used. When mouse fuzzies no longer seemed substantial enough, rat pups were offered instead. There was no change in feeding response transitioning from mice to rats. Eventually, barely weaned rats were offered at the rate of one rat per snake every 7 days. Once a regular feeding regimen was established, those animals continued to become more bold and aggressive feeders. They will now accept medium to large sized pre-killed rats every 7-10 days.
When multiple small, warm-blooded prey do not elicit a feeding response after a few consecutive attempts, other techniques may need to be considered. Occasionally mice or rats can be “scented” by rubbing a lizard, bird, or fish on it to transfer their scent to the rodent. In my experience mangrove snakes do not fall for this ruse. Rather, it seems to be a combination of size, shape, smell, and movement that ultimately encourages them to feed.
If all else fails, offering live frogs, fish, or small birds may be necessary. While rare, it is not unheard of to come across a Boiga that will steadily refuse all manner of prey until just the right flavor comes along. Although it is far from ideal, offering mangrove snakes prey that is inconvenient or difficult to procure is still preferable to the snake not eating at all. Many times, once a mangrove snake has had a series of 5-10 meals, it will become less finicky about its dietary preferences.
I will mention that it is extremely uncommon for any species of snake to fast until it dies of starvation. If the habitat is acceptable, and all other potential issues (both external and internal) have been ruled out, it is likely that given time and patience, the snake will begin to feed regularly.
In Closing
Mangrove snakes have fascinated me since I first saw one in person nearly 15 years ago. The beautifully contrasting colors, brilliant iridescence, and the allure of owning a rear-fanged snake all contributed to what has become a long-term obsession. While not impossible, captive reproduction of this species is sporadic at best. I sincerely hope that the information shared here will allow more individuals to become involved with these animals and strive to establish diverse breeding colonies.
Mangrove snakes are certainly not the easiest snake to keep, and are by no means recommended for neophyte snake keepers. They present even the most experienced keeper with a unique set of challenges and fairly exacting requirements. However, if you are up for the challenge, I can assure you, it is well worth it.
