Fea's Pitless Pitvipers - Reptilenesia

Late one spring night in 1887 in the Kakhyen Hills of Burma, 35-year-old Italian explorer Leonardo Fea crested a karst outcrop and entered a bamboo thicket. He barely noticed the rain, because before him lay a two-foot-long snake of indescribable beauty. It was shiny, dark purplish-black and marked with thin, widely-spaced neon orange bands so bright they almost  looked white. The head bore a striking symmetrical pattern of orange, gold, and black. When Fea picked the snake up, he saw that it had a plain purple belly. It appeared to be a harmless colubrid, and luckily for Fea, he wasn't bitten, so he had no opportunity to find out that it wasn't.

Fea was among the many European explorers and natural historians who were pouring into the newly-annexed nation of Burma, whose cultural roots date back to the 2nd century BCE. He collected thousands of vertebrates there for the Genoa Civic Museum, but perhaps none so unique or amazing as that snake. When Belgian-British herpetologist George Boulenger received a loan of Fea's reptiles from the museum, he declared of the single specimen "I may well say that Azemiops is the most interesting ophiological discovery made since that of Dinodipsas [Causus]¹". Boulenger described it as a new genus and species in his 1888 report on Fea's expedition, writing "it affords me great pleasure to connect with [this snake] the name of the courageous and highly successful explorer to whom science is indebted for this and so many other additions." Azemiops feae was the first species named for Fea, who was soon to also receive the honors of an eponymous petrel, tree rat, and muntjac, collected with his "untiring zeal" in southeast Asia and the Cape Verde islands.

Azemiops feae. Notice the enlarged head scales and the absence of a heat-sensing facial pit.

The enigmatic “pitless pitviper,” Azemiops feae or Fea's Viper looks almost nothing like other vipers, with its elliptical head, enlarged head scales, and smooth dorsal scales. In fact, it is so unusual that at times it has been classified as an elapid or a colubrid instead, of which its enlarged head scales in particular are reminiscent. Morphological and molecular evidence point to an ancient relationship between Fea's viper and other old world vipers ("viperines"), which last shared a common ancestor over 56 million years ago. Rather, Fea's viper is more closely related to the crotaline vipers, or "pit vipers", a predominantly New World clade that includes rattlesnakes, copperheads, and bushmasters (although even from these it is distinct, having diverged over 32 million years ago). Although there are a few other Asian crotalines, such as Hypnale and Trimeresurus, even these are more closely related to their New World counterparts than they are to Fea's viper, all sharing an infrared-sensitive facial pit. Indeed, Azemiops occupies a lonely branch of the snake family tree.

We know a little of the natural history of Fea's viper. It is found primarily in karst systems in the tropical uplands of northern Burma, northern Vietnam, and south-central China. Adults are active predominantly during cool, rainy summer nights, when they move slowly through deep leaf-litter in bamboo and tree fern thickets interspersed with well-lit clearings. They spend much of their lives in the holes and crevices of karst outcrops and in open and underground streams. Juveniles are most active on cool, wet fall nights. Like other vipers, Fea's viper hibernates in winter, so presumably they are fairly predictable in space and time when entering and leaving their hibernacula. Only a few prey items have been recorded, all of which have been rodents and shrews abundant in karst outcrops associated with swift mountain streams, although these snakes will also eat geckos in captivity.