The Slender Silver Boa

Scientists Discover New Snake Species in the Bahamas
May 26, 2016

Meet the newest snake species in the world: the Conception Bank Silver Boa or Chilabothrus argentum.

UNC-Asheville biologist Graham Reynolds, along with a team from the Harvard University Museum of Comparative Zoology found the slight, silver snake on a small uninhabited island in the Bahamas about 200 miles southeast of Nassau called Conception Island.

The silver boa is the first new species discovered in the Caribbean since 1942 and brings the total number of “West Indian” or “Rainbow” boa species to 12. 

Bahamas“It’s a tangible example of what a species is, how we describe them and how we define them,” Reynolds said in a press release.

The silver boa itself long and skinny, measuring between six and nine feet long but weighing in at about half a pound. Like its famous cousins, the boa constrictor and the anaconda, the silver boa is a non-venomous constrictor, squeezing its prey until they can no longer breathe.

While the silver boa is in the same family as the giant boa constrictors and anacondas, it is more closely related to the similarly sized rainbow boas of its own genus

Unlike its three closest relatives, the Northern Bahamas boa, the Bahamas boa and the Southern Bahamas boa, the silver boa is marked by its light gray to tan coloring and relative lack of other color patterning. The other three Bahamian boas have large dark spots or stripes, but the silver boa only has a faint, light gray stripe down its back and a few very small dark spots.

Also unlike the other Bahamian boas, the silver boa is primarily arboreal, meaning that it lives mostly in trees. Some of the boas Reynolds found had coiled themselves around one branch while reaching out for another with their heads, a technique many climbing snakes employ to get around in trees and shrubs.

Reynolds first discovered the silver boa on a July 2015 expedition to survey uninhabited islands in the Bahamas for nocturnal reptiles. They found the first silver boa halfway up a short palm tree. Over the next two days, they found five more silver boas, all in trees except for the last one, which crawled onto Reynolds’s head as he slept on the beach.

“It was incredible!” Reynolds said. “I’ve never had that happen to me before and haven’t heard of it happening to anyone else. When I first woke up I was a bit confused, but quickly realized it was a boa and started laughing out loud. I put the animal in a cloth holding sack until daylight to take measurements from it, and thought to myself that I might wake up in the morning and find that I had dreamt the encounter. But sure enough, there was the boa in the bag!”

Graham ReynoldsReynolds and his team captured and took body measurements of each silver boa before letting them go. They returned in October 2015 and found an additional 14 snakes, which they also measured and placed electronic tags on so they could be identified in the future.

DNA taken from silver boa tissue samples showed that the silver boas are a genetically distinct species. Reynolds compared the silver boa’s DNA for a specific mitochondrial protein—a sort of industry standard for separating species of boas—to DNA from other boas. The closest matches were to the three Bahamian boas, but the 3.3 to 5.4 percent difference in the DNA was enough to confidently set the silver boas apart as their own species. To get that difference, Reynolds and his colleagues estimate the silver boa diverged from the other three about 2.7 million years ago.

As exciting as the discovery of this new species is, there is a dark cloud hanging over the silver boas and its name is extinction. 

The researchers noticed several factors on the island that could potentially spell real trouble for the silver boa, first and foremost being the extremely limited range where these snakes are found. Reynolds and his colleagues estimate that silver boas have a range of less than five square miles.

What that means is any significant threat to the silver boa is made even worse by the fact that these snakes have nowhere to run and nowhere to hide. 

And it turns out that the boas do have at least one such threat in, of all things, cats. Not jaguars or panthers or ocelots but formerly domestic cats that find their way to these islands and turn feral.

“Cats end up on even the most remote islands, and we are often not sure why,” Reynolds said. "Sometimes it is by accident, and sometimes people intentionally release cats, perhaps because they think they are helping them.”

South Bahamas Boa

While some people might find snakes frightening, West-Indian boas are utterly defenseless against a common housecat, and feral cats on remote islands will gladly kill and eat the boas. The researchers discovered feral cats on the same island as the silver boas.

Another threat comes from poachers. Poachers commonly take many species of boa from the Caribbean to sell as pets. Boas from the rainbow boa genus, to which the silver boa belongs, can sell for thousands of dollars, and poachers already visit Conception Island for sea turtles. 

In the paper describing the silver boa, published in the journal Breviora, Reynolds and his colleagues write, “We are extremely concerned that the discovery of a new boa could elicit poaching activity . . . we intentionally refrain from describing exact localities or habitats [where the boas were found] for this reason.”

The researchers recommended that the silver boa be listed as critically endangered and are working with organizations like the Bahamas National Trust to conserve this new species.

“We found this species on its way to extinction, and now we have the opportunity to intervene on their behalf so that doesn’t happen,” said Reynolds.

That conservation effort includes more research. The discovery of a new species often poses more questions than it answers. Scientists still need to discover what silver boas eat, how they live and get a better idea of how many of them there are.

Reynolds says he will continue to lead expeditions to the Bahamas to learn more about these snakes, and hopefully keep them around now that we know they are there.

—Daniel Lane

Daniel Lane covers science, medicine, engineering and the environment in North Carolina.