How Spiders Keep The Peace

Credit: Francis Ratnieks

By Nisha Giridharan

The Parawixia bistriata (pictured), a large spider that lives in the semiarid habitats of southern Brazil, knows that when it comes to living in a crowded neighborhood, fighting is never the answer. 

Scientists knew that communities of P. bistriata emerge from collective shelters at sunset and build individual webs along permanent and communal silk support lines. 

At the end of the night, however, a small number of webless spiders peacefully share the prey of their neighbors—a rare instance of cooperation among arachnids. 

Now, after months of observation, researchers have developed a new model explaining the behavioral strategies of these webless spiders. 

Once the sun begins to set, P. bistriata swarm the communal silk lines, searching for spots to build their webs. As each spider claims its territory, it shoos away others that try to settle uncomfortably close by. Early in the evening, the still-webless interlopers graciously move on, knowing that they will likely find an empty spot elsewhere. But as the night progresses, desperation sets in. Open sites become scarce, so webless spiders no longer retreat when resident spiders bounce up and down to drive them away. Instead, they sit near a resident's web and freeload on large prey—seemingly with the resident's permission. 

Applying insights from game theory, the researchers concluded that resident spiders don't aggressively defend their territory because a night's meal is not worth risking their lives in a fight, they report this month in The American Naturalist. 

What's more, any spider could find itself on the other side of the negotiation the next night, when the race for space begins again. 

Spiders Hunting In Packs

Tarantula The Size Of A Human Face Discovered

Its legs, which have unique daffodil-yellow markings, span a massive 20cm (eight inches). The arachnid also has a distinctive pink band around its body.

The new species was found in the war-torn north of the South Asian country by scientists from Sri Lanka's Biodiversity Education and Research (BER) organisation.

It has been named Poecilotheria rajaei, in recognition of a senior police officer called Michael Rajakumar Purajah who guided the research team through a hazardous jungle overrun by civil unrest in order to seek out the spider.

The spider is said to prefer living on old trees

The arachnid had originally been presented to BER three years ago by villagers in Mankulam who had killed a male specimen.

Scientists immediately realised the dead spider was not like anything they already knew and a group was charged with finding any living relatives.

The living Poecilotheria rajaei were eventually discovered in the former doctor's quarters of the village's hospital.

According to wired.com, Ranil Nanayakkara, the co-founder of BER, said: "They are quite rare.

The tarantula is characterised by its yellow legs and pink band

"They prefer well-established old trees, but due to deforestation the number have dwindled and due to lack of suitable habitat they enter old buildings."

The website described the tarantula as "colourful, fast and venomous".

The species is said to be related to a class of South American tarantula that includes the Goliath bird-eater, one of the world's largest spiders.

In other reports Mr Nanayakkara is quoted as saying none of the tarantulas found in Sri Lanka have bites that are deadly to humans. However, the Poecilotheria rajaei would be able to kill animals as large as mice, lizards and small birds and snakes.

A male member of the Poecilotheria rajaei species

Peter Kirk, who covered the discovery for the British Tarantula Society's journal, told Sky News: "Ranil has been working on these spiders since 2009 out in Sri Lanka and this is the first of what is thought to be a number of new species he has discovered in what was previously the inaccessible northern region of the island.

"It demonstrates that wildlife continues to survive whilst we are in the throes of conflict and that they can adapt to its changing environment - but also highlights that we risk destroying the habitats of species new to science and condemning them to extinction before they are even discovered."

Source: Sky News

The Net-Casting Spider

A scene from the BBC's "Life in the Undergrowth" showing a tight triangular net used to catch a fly and a net-casting (Deinopidae) spider fishing a cricket with a "cobweb sack" using its own legs.

The Spider That Builds Its Own Spider Decoys

A spider that builds elaborate, fake spiders and hangs them in its web has been discovered in the Peruvian Amazon.

Believed to be a new species in the genus Cyclosa, the arachnid crafts the larger spider from leaves, debris and dead insects. Though Cyclosa includes other sculpting arachnids, this is the first one observed to build a replica with multiple, spidery legs.

Scientists suspect the fake spiders serve as decoys, part of a defense mechanism meant to confuse or distract predators. “It seems like a really well evolved and very specialized behavior,” said Phil Torres, who described the find in a blog entry written for Rainforest Expeditions. Torres, a biologist and science educator, divides his time between Southern California and Peru, where he’s involved in research and education projects.

“Considering that spiders can already make really impressive geometric designs with their webs, it’s no surprise that they can take that leap to make an impressive design with debris and other things,” he said.

In September, Torres was leading visitors into a floodplain surrounding Peru’s Tambopata Research Center, located near the western edge of the Amazon. From a distance, they saw what resembled a smallish, dead spider in a web. It looked kind of flaky, like the fungus-covered corpse of an arthropod.

But then the flaky spider started moving.

A closer looked revealed the illusion. Above the 1-inch-long decoy sat a much smaller spider. Striped, and less than a quarter-inch long, the spider was shaking the web. It was unlike anything Torres had ever seen. “It blew my mind,” he said.

So Torres got in touch with arachnologist Linda Rayor of Cornell University who confirmed the find was unusual. “The odds are that this [species] is unidentified,” she said, “and even if it has been named, that this behavior hasn’t previously been reported.” Rayor notes that while more observations are necessary to confirm a new species, decoys with legs — and the web-shaking behavior — aren’t common in known Cyclosa. “That’s really kind of cool,” she said.

Afterward, Torres returned to the trails near the research center. Only within a roughly 1-square-mile area near the floodplain did Torres find more spider-building spiders — about 25 of them. “They could be quite locally restricted,” he said. “But for all I know, there’s millions of them in the forest beyond.” The spiders’ webs were crafted around face-height, near the trail, and about the width of a stretched-out hand. Some of the decoys placed in the webs looked rather realistic. Others resembled something more like a cartoon octopus.

“I have never seen a structure just like this,” said William Eberhard, an entomologist at the Smithsonian Tropical Research Institute and University of Costa Rica who studies spiders and web-building.

Though Cyclosa are known for building decoys, most of the described spiders’ constructions are clumpy, made out of multiple little balls built from egg sacs, debris or prey, rather than something resembling an actual spider. “Known Cyclosa don’t have that spider-with-leg looking thing, which is why we think it’s a new species,” Torres said.

But without a permit to collect any organisms, anatomical confirmation of the new species is on hold. 

Torres is returning to the site in January, and will be able to collect some spiders then. Eberhard notes that identifying a new species based on the decoy-building behavior alone is probably not possible. 

“Species are distinguished on the basis of the structure of the male and female genitalia,” he said. “To a lesser extent, on the overall abdomen shape.”

Via: "Wired"