Hunters gain the upper hand if they remain undetected by their prey until it’s too late, and camouflage is a great way to stay hidden. A novel camouflaging behavior has been identified in a wee jumping spider for the first time, with the artistic arachnid decorating its nest until it practically morphs into a cloak of invisibility.
The jumping spider Arasia mullion is the visionary behind the behavior, and is the focus of a paper published in PeerJ. The authors of the study carried out field surveys in A. mullion’s home of eastern Australia, during which time they watched around 115 spiders build 554 silk retreats – an impressive feat considering how easy they could be to miss.
The webslingers are pretty creative as living quarters go, and these silk creations fall under these animals’ “extended phenotypes,” a term used to describe the way a creature’s nest can form part of their characteristic traits. For some, that may be vast social webs in which spiders hunt in packs, others dangle on simple structures with a net ready to catch passing prey.
A. mullion first caught the researchers’ eyes as they noticed there were a surprisingly large number of them on tree trunks, and that they would hang out in their silk nests during the day, unlike most jumping spiders which go wandering.
"I was actually looking for a different group of spiders that camouflaged their bodies also in the surface of tree trunks when I noticed them," said study author Alfonso Aceves to IFLScience.
"It’s interesting that there’s a lot of these camouflaged retreats (or blankies as we like to call them in the lab) in parks in urban areas in Sydney. The tricky part is that from a distance - maybe from 2 meters - nothing would make you pay attention to the blankies. They look just as part of the tree. But because I was always looking at the trees from a short distance, I saw these tiny spiders peeking and looking at me before retreating to the inside their blankies."
"That’s when I got hooked and later I checked many of these suspicious “marks” on the trees. Soon after I knew there was something special going on."
Curious, Aceves and colleagues captured around 20 spiders, removed their nests, and released them so they could film the nest’s construction.
The footage revealed that blankies use their nests as an opportunity to get creative, incorporating chunks of its local environment to create a mosaic that camouflages the nest.
The spiders would gather bark by carving it off the tree, creating a scar elsewhere on the trunk, before dashing back to the nest and flipping upside-down to brush the pieces across the silk nest’s underside. The overall effect creates what Aceves calls an "invisibility blankie".
The attention to detail might seem like a lot of effort, but unlike more nomadic spiders it appeared these animals were reliant on their silk, camouflaged nests as their permanent residence. Therefore, it figures to put a lot of effort into your decor if you’re going to be spending a lot of time there.
“We found that Arasia mullion led a sedentary life on the surface of tree trunks, where they build, decorate, and occupy their silk retreats,” wrote the study authors.
“These findings are the first description of silk decorating behaviour in jumping spiders, and highlight the unusual use of permanent silk retreats to exploit a low complexity and highly exposed environment. Our study puts a research lens on tree trunks as understudied but highly intriguing habitats.”