For thousands of years a thin bridge of sand and rock connected mainland India with the island of Sri Lanka. The 30-kilometer stretch known as Rama’s (or Adam’s) Bridge disappeared centuries ago—probably after a cyclone in the year A.D. 1480—but its legacy remains today. Nowhere is that more evident than on one of the few pieces of Rama’s Bridge that still exists: the tiny Sri Lankan island of Mannar.
Few people visited Mannar during the 25-year Sri Lankan civil war—a bloody insurgency that killed around 100,000 people and ended in 2009—so the greater flamingos, oystercatchers, pied avocets and other birds that nest there remained undisturbed for decades, along with other rare plants and wildlife. And according to a February 4 paper in the Journal of Asia-Pacific Biodiversity, something else has been hiding there for centuries—since long before Rama’s Bridge disappeared.
The revelation began in 2012. That’s when a team of researchers from the University of Kelaniya in Sri Lanka was conducting a survey of some of the country’s more than 500 known spider species. In a hollow tree on Mannar they found something that no one in the island nation had ever seen: a large, colorful tarantula called the Rameshwaram ornamental (Poecilotheria hanumavilasumica).
Now, this ornamental tarantula is not new to science. The 22-milimeter-long species was actually discovered 10 years ago. But it was named after—and had only been seen near—the Indian town of Rameshwaram. It’s critically endangered, with eight isolated population groups totaling just a few hundred individuals. The tarantulas inhabit less than 10 square kilometers of land scattered over a total distribution of about 100 square kilometers.
Rameshwaram itself is located on a small island at the tip of the Indian peninsula, and according to legend it’s where the Hindu god Rama started construction of the bridge to Sri Lanka. The paper’s researchers say that the former land bridge would have allowed the species to range more broadly before the populations became separated.
Although the dry conditions and vegetation in some parts of Mannar match what can be found in Rameshwaram, the spiders appear to be even rarer on the island. The researchers only located four females and eight spiderlings. No males were spotted but one of the females carried an egg sac, so reproduction is obviously occurring.
What else might turn up on Mannar? The researchers think there may be other discoveries waiting. The island has been scientifically neglected for 30 years because of the civil war and resulting long-lasting resentments, so there’s plenty of flora and fauna left to document.
Unfortunately, the time in which to do so may be limited. Factories and other commercial developments have started to pop up on Mannar, including a large project that is about to begin on the edges of the forest where the tarantula was discovered. The researchers hope that the discovery of the Rameshwaram ornamental tarantula could help to slow that down by providing new incentives to conserve the island.
Photo (uncredited) from the paper by Nanayakkara RP, Ganehiarachchi GASM, Vishvanath N, Kusuminda TGT
Previously in Extinction Countdown: