Some cannibal pirate spiders trick their cousins into ‘strolling the plank’

A Costa Rican pirate spider lives as much as the household identify: It methods carefully associated orb weaver spiders into “strolling the plank,” proper to their doom. 

The world’s many pirate spiders exploit a really explicit meals supply — different spiders. However whereas most pirate spiders invade the webs of different arachnids, Gelanor siquirres dupes potential prey into building a web right into a trap, researchers report in an upcoming Animal Behaviour.

Like several respectable pirate, pirate spiders have an intensive bag of methods. Some species delicately strum the threads of different spiders’ webs to persuade the arachnids they’ve caught an insect, solely to strike when the online proprietor comes to gather its prey. Others mimic on an online the signature rhythms of a distinct spider’s courtship dance, luring would-be suitors to their deaths.  

On a visit a number of years in the past to a organic reserve in Costa Rica, researchers had been the primary to witness a hunt by a little-known species known as G. siquirres. It cleverly exploits the way in which different spiders make their webs to get a meal, the group realized.

At dusk within the steamy lowland rainforests of Costa Rica, orb weavers let free “floating strains” — single strands of silk that blow within the breeze till the free finish sticks on one other floor, akin to a tree department. The orb weaver then scurries throughout to safe the second anchor level, and this primary moored line serves as the muse for the online.

However when G. siquirres strikes, the orb weaver doesn’t scuttle throughout this bridge line to some welcoming vegetation. As an alternative, it walks right into a entice; G. siquirres has already forged its personal silk strains, not with the intention of constructing an online, however to intercept that of the orb weaver.

Throughout their journey, arachnologist Laura Segura-Hernández and colleagues stumbled on a perplexing scene: An uncommon configuration of a number of strands of silk converged at a single leaf. The group additionally observed one other spider’s floating line caught on a kind of strands. Then, because the floating line’s proprietor — a juvenile orb weaver — scuttled throughout, a pirate spider emerged from behind its leaf hideout and crept down towards the intersection.

In all probability feeling vibrations from the approaching pirate spider, the orb weaver hooked up a dragline — the arachnid’s model of a bungee wire — and flung itself off its bridge line. The pirate spider was shut on its heels, pursuing from its personal dragline.

“They’re hanging there, combating,” says Segura-Hernández, who lately completed her Ph.D. on the College of Nebraska–Lincoln. It was a dramatic scene, she says, like two swashbuckling pirates exchanging blows whereas swinging from the rigging. The encounter ended with a surprisingly swift assault from the pirate that immediately immobilized its prey.

The searching technique comes as a complete shock, says Gustavo Hormiga, a biologist at George Washington College in Washington, D.C., who helped identify and describe G. siquirres in 2016. Exploiting how different spiders construct their webs is “truly fairly refined,” he says. “I don’t know of something like that in any [other] spider group.”

This new research helps convey G. siquirres to life, Hormiga says. Till now, the spider was recognized to science by solely a lifeless specimen collected in 1994.

The discovering additionally underscores the necessity for old-school pure historians, Hormiga says, the form of scientists who wander out at evening with a head lamp to see what there’s to search out. “For many people, that is actually what introduced us into science,” he says. “Not pipetting. Simply being on the market.”