The Philippines is home to five known species of pit vipers* distributed rather evenly across the archipelago, particularly in high rainfall areas. Many of these snakes are found near human habitation, and although bites are seldom heard of, they do occur nonetheless, although those resulting in fatalities seem rare.
Let’s look into one of the most common of our pit vipers, Tropidolaemus subannulatus.
Because this and other arboreal vipers are often encountered by locals, they have become familiar enough to warrant recognition in the native vernacular. In many parts of the Tagalog region, pit vipers are often called mandadalag due to the belief that these snakes feed on dalag (snakeheads or Channa ssp.), a supposition that stemmed from observations of these snakes waiting in ambush on low bushes over bodies of water.
However, these arboreal vipers, as far as is known, do not feed on fishes. Another name applied, though less common, is tres kantos, which is an obvious allusion to the prominently triangular heads. Additionally, these are called rupong or dupong in the Bicol region and in the Visayas, and as papala in northern Mindanao. The Bicolano and Visayan name is similar to the Tagalog ulupong which applies on cobras; it may be that the term is a catch-all for venomous snakes, or even those perceived to be.
The best known species, T. wagleri, is often called “temple viper” as these are often placed and revered in temples in parts of Southeast Asia. The two Philippine species are referred to as “Philippine temple viper”, but I find this designation ambiguous due to the simple fact that there are very few temples here, and that none are known to have these snakes around.
Another variation is “Bornean keeled pit viper”, which doesn’t really make sense considering that the species is not found only on Borneo. Perhaps the name “keeled pit viper” suits this species just fine.
Ambiguity in Variety
Tropidolaemus subannulatus typically reach total lengths of almost a meter, but some Philippine specimens are small, seldom reaching a total length of 60 centimeters for females, with males attaining only about a third of that measurement.
Ground color is green to dark green with narrow crossbars of russet edged with white, although in some populations, these crossbars are diminished into short, vertical dashes. A post-ocular (behind the eyes) stripe of russet and white is also present. The ventrals have pairs of whitish spots that encircle a smaller red dot. Dark green individuals have the russet stripes substituted with purplish-brown. In Negros and Calamian populations, the ground color is bluish-green with the russet bands replaced with chalky blue edged with pale blue instead of white.
Incidentally, these blue animals also grow larger and more robustly than any other population in the Philippines; it is likely that these snakes are distinct and may prove to be an independent species, pending further investigation.
A rare color variation is one where the ground color is yellow, with very thin purplish-brown and pale yellow banding.
Like many other arboreal vipers, the tails of Tropidolaemus are differently colored, due to their use in caudal luring wherein the tails are waved to fool potential prey into thinking that these are worms or caterpillars. I am yet, however, to observe this behavior in captive snakes.
Tropidolaemus subannulatus is not restricted to the Philippines, and has been recorded in Borneo and Pulau Belitung, as well as Buton, the Sangihe Archipelago, and Sulawesi in Indonesia, according to a 2007 paper by Gernot Vogel and team published in Zootaxa.
In the 1986 book entitled Guide to Philippine Flora and Fauna Philippines, Alcala noted their presence in the islands of Balabac, Basilan, Bohol, Dinagat, Jolo, Leyte, Luzon, Mindanao, Negros, Palawan, Panay, Samar, Sibutu, and Tumindao, but one should be aware that this listing was done at a time when all Philippine Tropidolaemus were still understood to be under a single species. Still, entities from across this range may be accorded separate species status once a full evaluation of all examples are undertaken.
The only other species of Tropidolaemus present in the Philippines is T. philippensis, known from Leyte, Samar, and southern and western Mindanao, although T. hombronii, found originally on Zamboanga, may need to be reinstated from being a synonym of T. philippensis and there may be populations that could be distinct enough to permit recognition at the species level. True T. wagleri, as far as is currently known, does not exist in the archipelago.
Male or Female?
In other parts of the species’ range, females display a range of coloration, usually with a yellow background with scales edged with blue or blue-green, resulting in a reticulated pattern, plus crossbars of the same color. Males are bright green with russet stripes edged with white, in varying breadths.
Philippine snakes have both sexes appearing the same color-wise, although it is possible that the southern populations have the females very similar in pigmentation to those from neighboring countries.
It has been repeatedly said that one can determine the sex of these snakes based on the eye color, with females having yellow to orange eyes while it is silvery white in males — and vice versa, depending on who you are conversing with. However, it is my observation that there exists a great deal of overlap that gauging a snake’s sex based on eye color alone can result in errors.
Snaking their way out of conflict
In herpetocultural circles, these snakes are often touted as notoriously placid, and this observation is not without some grain of truth.
Compared to other venomous snakes, and to arboreal vipers in particular, Tropidolaemus are much more laid back. Observations on captive snakes show that T. subannulatus often make mock strikes with the mouth closed, and only when sufficiently antagonized will these snakes attempt to bite defensively. However, many individuals will only attempt to hide their heads when agitated.
Compared to other arboreal vipers, T. subannulatus, as well as its relative T. wagleri, can be free handled chiefly by the most seasoned herpetoculturists.
Members of this genus exhibit very strong site fidelity, often staying for extended periods of time in just a single spot waiting for prey to come by. Not surprisingly, their metabolism is very slow and allows the snake to go without feeding for many weeks at a stretch.
Due to their preference for higher rainfall areas, these as well as members of the genus Trimeresurus have adapted to drinking from rainwater collected on leaves and even from their own coils. In heavy downpours, these vipers have been seen to slightly lower their heads to facilitate the flow of rain water into their mouths.
These nocturnal snakes take both endothermic and ectothermic prey, and will feed on birds and small mammals, mostly rodents, as well as geckos, sleeping agamid lizards, and frogs. Being able to detect heat from endothermic animals, it is possible that these pit vipers can utilize chiropteran (bat) prey but this remains to be fully documented. These snakes are ovoviviparous, which means that the eggs develop inside the females’ body and is nourished not by placental attachment, but by an egg yolk.
Striking a Nerve
I am not aware of in-depth studies done on the nature of T. subannulatus venom, but in the related T. wagleri, it has been shown that in stark contrast to those from most other viperids, their venom is mainly neurotoxic, as detailed by Choo Hock Tan and colleagues in a 2017 article for Scientific Reports.
Neurotoxic venom is commonly found in the family Elapidae, which includes the planet’s venomous heavyweights: cobras, taipans, and mambas. Viper venom is typically cytotoxic, which results in tissue damage rather than an attack on the nervous system.
Nonetheless, it must be noted that reports of lethal bites of Tropidolaemus on humans appear non-existent.
Compared to neighboring regions, there are fewer published studies done on Philippine snakes, venomous ones including. Much work done locally is centered only on distribution and venomous snakes’ medical significance, but practically nothing on other aspects such as prey spectra and population densities.
Thankfully, though, systematists have been focusing on determining the identities of the varied populations so that we may finally have a better understanding of our pit viper diversity, although a great deal of work still needs to be done. Optimistically, gaps in our knowledge will be filled in by upcoming herpetologists and locals who see fascination in these snakes, instead of trepidation and fear.
Tropidolaemus was established by German physician and zoologist Johann Georg Wagler in 1830 but subsequent workers preferred that it be maintained under the genus Trimeresurus.
In my youth, I have recurrently consulted Dr. Alcala’s Guide to Philippine Flora and Fauna, where both T. subannulatus and T. philippensis are referred to as Trimeresurus wagleri, a treatment in line with Leviton’s view, as detailed in the latter’s 2014 book, “The Dangerously Venomous Snakes of the Philippine Archieplago with Identification Keys and Species Accounts”. In 1996, Kraus, Mink, and Brown resurrected the genus, a line of thought still followed to this day. Tropidolaemus differs significantly from members of the latter genus by its strongly keeled gular (throat) scales, small and keeled scales on the head, absence of a nasal pore, and a hemipenis that is actually closer to terrestrial pit vipers (Calloselasma, Deinagkistrodon, and Hypnale) than it is to other arboreal vipers.
The specimen used to describe the species was collected by the Englishman Hugh Cuming, who also collected great numbers of shells as well as plants from the Philippines from 1836 to 1850, and which were later described as new species; Cuming did not designate a specific locality for his specimens, choosing instead to label these as simply from the “Philippines”.
The species was formerly described as Trimesurus subannulatus by John Edward Gary in 1842. In 1864, Albert Karl Ludwig Gotthilf Günther placed the taxon in the synonymy of Trimeresurus wagleri — a decision which was followed by many subsequent authors and which stood for many decades.
As mentioned above, the populations from Negros differs from what is perceived as T. subannulatus, an anomaly that was rectified by Edward Taylor when he described Trimeresurus wagleri alboviridis in 1917, based on specimens he collected two years earlier from Isabela, Negros Occidental. In due time, if these animals from that island are granted an autonomous status then these will be referred to as Tropidolaemus alboviridis.
This appeared in Animal Scene magazine’s January 2019 issue.