Scientists have found the world's largest species of golden orb-weaver spider in the tropics of Africa and Madagascar. The discovery marks the first identification of a new Nephila spider since 1879.

Females of the new species, Nephila komaci, measure a whopping 4 to 5 inches in diameter, while the male spiders stay petite at less than a quarter of their mate's size. So far, only a handful of these enormous arachnids have been found in the world.

"We fear the species might be endangered, as its only definite habitat is a sand forest in Tembe Elephant Park in KwaZulu-Natal," ecologist Jonathan Coddington of the Smithsonian's National Museum of Natural History said in a press release. "Our data suggest that the species is not abundant, its range is restricted, and all known localities lie within two endangered biodiversity hotspots: Maputaland and Madagascar."

The first potential specimen of the new species was uncovered by Coddington and his colleague Matjaz Kuntner of the Slovenian Academy of Sciences and Arts in 2000. They found a huge female orb-weaver among a museum collection of spiders in Pretoria, South Africa, and she didn't match the description of any known spider. Although they hoped the unusual-looking giant represented a new species, several dedicated expeditions to South Africa failed to find any live spiders of a similar description.

Then, in 2003, a second specimen from Madagascar was found at a museum in Austria, suggesting that the first spider hadn't been a fluke. But despite a comprehensive search through more than 2,500 samples from 37 museums, no additional specimens turned up, and the researchers assumed the biggest of all orb-weavers was probably extinct.

Finally, three live spiders have been found to prove the scientists wrong: A South African researcher found two giant females and one male in Tembe Elephant Park, proving that the new species was not extinct, just incredibly rare.

"Only three have been found in the past decade," Kuntner wrote in an e-mail to Wired.com. "None by our team, despite focused searches. Only an additional two exist in old museum collections. Compared to thousands of exemplars of other Nephila species in museums, that is disproportionately rare."

The two biologists named the new species after Andrej Komac, a scientist friend of Kuntner's who died in an accident near the time of the discoveries.

Like all Nephila spiders, females of the new species spin huge webs of golden silk, often more than 3 feet in diameter. In the report of the discovery of this rare spider, published Tuesday in PLoS One, the researchers also addressed the evolution of the dramatic size difference between male and female orb-weavers.

By mapping out the evolutionary tree of all known orb-weaver species, the scientists discovered that as the spiders evolved, females got bigger and bigger, while males stayed roughly the same size.

"It is good for females to be big, because they can lay so many more eggs," Coddington wrote in an e-mail. In addition, large size probably helps females avoid being eaten by predators.

"Relatively few groups can safely pluck an orb-weaving spider from its web," he wrote, "because you have to be able to hover to do so (hummingbirds, wasps, damselflies come to mind). None of these are large enough to tackle an adult Nephila, or even a large juvenile."

Males, on the other hand, are better off staying small and reaching sexual maturity at a young age. Going out searching for a mate is one of the most dangerous activities they undertake.

"So males risk everything to find, probably, just one, huge female, inseminate her, and probably do not willingly leave her web to search for another," Coddington wrote. "Nothing about sex says males must be big."

Image 1: Tiny male Nephila spiders are dwarfed by their female counterparts. Matjaz Kuntner and Jonathan Coddington/PLoS ONE.

Image 2: A giant golden orb-web exceeding 1 meter in diameter, spun by a Nephila inaurata spider. M Kuntner.

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