A spider whose characteristic mating display has been familiar to UAE naturalists for at least a quarter of a century has finally been officially recognised by science. While the newly named Wadicosa arabica, a type of wolf spider, has long been known locally, it was a collaboration with a spider expert in Sweden that resulted in the creature being officially identified.
Among the authors of a new paper describing the creature is Gary Feulner, a Dubai-based lawyer from the United States, who has been exploring the outdoors in the UAE and writing about what he has found for more than three decades.
"They become one of many friends that anybody will make in the wadis or the mountains if you go out a lot. You will see many of the same creatures showing up again and again," he told The National. "I noticed this little fella who kept showing up in gravel wadis. It appeared to be distinctive."
"You have to get close to see how distinctive it is. The male is particularly conspicuous because when the males are seen they're usually on the gravel, cobbles, pebbles," he added. "When the males were out and about they were often on the prowl and they would be signalling by raising their two front palps."
Palps are the second pair of appendages on the spider’s head, sitting between the jaws and the first set of legs, and are roughly equivalent to the animal’s hands.
What makes this spider different?
"They [males] held their palps at a 90-degree angle like an elbow or human finger and they would raise them up and down," Mr Feulner said. "Because they had a bright white spot among the black, they were noticeable. It was always as if the spiders were signalling and of course they were signalling, but they weren't signalling to me. It was an endearing feature."
After a male makes a few up-and-down movements of his palps, he will typically move to another location and signal again. In their new study, published in Zootaxa, the authors note that the response of the female "has never been observed".
"Since observed courtships have never resulted in copulation, we are uncertain whether additional behavioural elements are involved in a typical courtship," the authors wrote.
The new publication, released last month, and the formal identification of W arabica, came about because Mr Feulner and another experienced naturalist and fellow member of Emirates Natural History Group, Binish Roobas, described and illustrated it among a number of other spiders in a 2016 paper. This was seen by Dr Torbjörn Kronestedt, of the Swedish Museum of Natural History in Stockholm, who realised it was the same species as an unidentified specimen from Oman.
The three authors collaborated on the new study, which gives the new species its name and describes its detailed anatomical differences from closely related spiders. In a more widespread Wadicosa species, W fidelis, the male also raises and lowers his palps in unison, but more slowly.
“It has a similar but not exactly the same mating signal – the male raises and lowers the palps but it’s slower, more relaxed and in most of the instances that we’ve seen, at least when we know females are present, the male stands up on what Professor Kronestedt has called the tip-toe stance,” said Mr Feulner, who has lived in the UAE for four decades.
“It’s as if you’re looking to impress somebody by standing taller and signalling with your palps more slowly. It’s a smaller species but it’s still impressive to see them standing up and trying to show off.”
Where has the Wadicosa arabica spider been sighted?
Where does this spider species live?
W arabica is usually limited to the vicinity of damp ground, such as on either side of pools of flowing water, and it will climb up on dry cobbles. The creation of dams in recent decades is thought to have given the creature additional suitable habitats.
"You see it typically because you're walking along and always watching your feet because you're on uneven ground," Mr Feulner said, adding that an eye-catching feature is the spider's ability to run across water. “You tend to see it if it moves across the rocks or across the water, or if it’s a male and it’s signalling, because you see the two little white flashes,” he said.
W arabica appears to live only in the Hajar mountains of the UAE and Oman, and has not been observed in the Musandam peninsula, where the different weathering pattern of the mountains means that surface water and streams, which create habitats that the spider likes, are much more rare. Mr Feulner said they could be “relatively abundant” in suitable habitats.
“If you’re seeing them in good numbers alongside water you might find three or perhaps four per square metre, mostly less,” he said. “We tend to see them after rains, which means mostly in the winter and spring, although we’ve also seen them in summer after summer rains.”
What happens to the spiders when conditions are very dry is unclear, although Mr Feulner said it was likely that the creatures, which are about 1cm to 2cm across including legs, have a prolonged period of dormancy.
“When the eggs hatch, the spiderlings cling in a sort of blanket to the abdomen of the female, who carries them around on her back for a period of time,” said Mr Feulner. “You sometimes see female spiders that look larger than usual. They look a little fuzzy and when you look a little closer, you see that the fuzziness is lots – dozens – of tiny spiderlings. That’s true in W arabica and in many wolf spiders.”
