World's largest web-spinning spider discovered in South Africa

In the forests of South Africa lurks an arachnophobe's nightmare - Nephila kowaci, the largest web-spinning spider in the world. The females of this newly discovered species have bodies that are 3-4 centimetres in length (1.5 inches) and legs that are each around 7.5cm long (3 inches).

This new species is the largest of an already massive family. There are 15 species of Nephila - the golden orb weavers - and at least 10 of them have bodies that are over an inch long. Many spin webs that are over a metre in diameter.

The first of these giants was discovered by Linnaeus himself in 1767 and the most recent one was described 140 years ago in 1879. Thousands of specimens have been collected and grace the displays and drawers of the world's natural history museums. But every attempt at finding a new Nephila species since 1879 (and there are more than 150 suggested scientific names on record) has been a dead end - the "new species" are always repeats of known ones.

All of that changed in 1978, when a new Nephila spider was collected at Sodwana Bay in South Africa. The unusual spider caught the attention of Matjaz Kuntner and Jonathan Coddington from the Smithsonian Institution. The duo launched several expeditions to capture the elusive spider but all of them failed. They were beginning to think that had found a hybrid, or a species that had become extinct since its brief flirtation with discovery.

Then, their fortunes changed in 2003, when they found a second specimen in an Austrian museum, taken from Madagascar. This was no hybrid. A few years later, three more surfaces - a female and a male collected in Tembe Elephant Park in South Africa. N.komaci was far from extinct, and clearly a new golden orb-weaver species, the first to be described for over a century. The duo named it after Kuntner's best friend, Andrej Komac, who died while these discoveries were made.

This is not the new species - it's Nephila clavipes. Unfortunately, no photos fo N.komaci were available. Look at the size difference between the female and the male though... 

Like other Nephila spiders, N.komaci's females are the giant ones. The male, by comparison, has a body that is less than a centimetre long and has legs that are 4cm long, no bigger than a large house spider.

With measurements of this new species, Kuntner and Coddington reconstructed the evolutionary history of this family of eight-legged giants. By building a family tree of the golden orb-weavers and related families of spiders, the duo showed that the females became increasingly large as the group diverged and evolved. N.komaci is the epitome of that evolutionary enlargement and is 7 times larger than the group's ancestor probably was.  

While the giant females all cluster around one part of the family tree, the males show no such patterns in terms of their size. Species with large males aren't any more closely related than they are to those with small males. These patterns strongly suggest that male and female Nephila have massive size differences between them because the females grew big rather than because the males shrank.

This family has much to teach us about the evolution of size differences between the two sexes - a trend that is commonplace throughout the animal world. And yet, its discovery comes with a familiar warning. It may well be already endangered. With only five individuals ever seen, it's hard to say, but the spider has only been found in two areas - part of South Africa and Madagascar - that are hotspots of endangered wildlife.

Reference: PLoS ONE 10.1371/journal.pone.0007516

More on spiders:

• Bagheera kiplingi - the mostly vegetarian spider
• Spider mimics ant to eat spiders and avoid being eaten by spiders
• Spiders gather in groups to impersonate ants
• Traumatic insemination - male spider pierces female's underside with needle-sharp penis
• Singaporean spiders spit venomous glue, work together, eat each other

Images: Photo  Victor Patel (not of the new species)