The exquisitely decorated abdomen of the mirror spider may resemble a disco ball, but the special effect is not just a flashy show.
The reflective jacket covering the spider’s abdomen scatters light and confuses potential predators, making it a defense mechanism that also looks quite spectacular.
A byproduct of the spider’s digestive activity, the mirror-like panels on its abdomen are made of the organic compound guanine, according to Find-A-Spider Guide author Ron Atkinson. The spider excretes crystals onto the surface of its back side somewhat like a mirrored mosaic, giving it a “disco ball” effect.
Theridiidae thwaitesia nigronodosa specimen from Mallacoota, Australia, pictured Jan. 21, 2015 (Courtesy of Ian Macaulay via Robert Whyte)
Australian spider expert and photographer Robert Whyte first noticed the mirror spider in its natural habitat reflecting the light of a small leaf. Whyte, who is a researcher for Queensland Museum, has amassed a huge collection of impressive closeup photographs since that first encounter.
Speaking to Australian Geographic, Whyte described its mirrored abdomen as “particularly good camouflage in the tropical areas where it rains more, because you have rain drops which also sparkle in the sun, and so the spider goes relatively unnoticed.”
A Thwaitesia nigronodosa specimen from North Queensland, Australia, on Nov. 12, 2014 (Courtesy of Ian Macaulay via Robert Whyte)
A Thwaitesia nigronodosa specimen belonging to the Entomological Society of Queensland's Bug Catch of March 16, 2014 (Courtesy of Robert Whyte)
The mirror spider can also contract its gut muscles over the guanine crystals, resulting in a rapid color change. “The stimulus for these muscle cell contractions is usually external,” such as from a predator, Atkinson told Science Friday.
“[R]eflections from the plates may resemble those from droplets of water in the green vegetation,” he added, “and the colored bits of the spider could easily be confused with flower parts.”
The mirror spider is a member of the Thwaitesia genus of comb-footed tropical spiders. Females are larger, measuring an average of 4.5 millimeters in length, and males measure 2.7 millimeters.
A lightning-fast runner, the mirror spider is also allegedly camera shy.
A juvenile Thwaitesia nigronodosa sporting a large black patch on its back photographed at Springbrook, Australia, on July 13, 2013 (Courtesy of Robert Whyte)
Meanwhile, Whyte maintains that the beautiful arachnid is changing public perception of Australian spiders amid the country’s reputation for hosting some of the largest in the world.
“These lovely little arachnids are hugely changing the way we think about spiders,” he told Australian Geographic. “When I show pictures of the mirror spider to people during talks, people will say, ‘Oh that’s beautiful,’ while other people who might be afraid of spiders say, ‘That’s not a real spider.’”
The spider expert believes that hope for change lies with the next generation, as the non-venomous mirror spider, with its unique, captivating sparkle, is particularly popular with kids.
A closeup Thwaitesia nigronodosa specimen pictured on March 6, 2015 (Courtesy of Ian Macaulay via Robert Whyte)
“Kids are not as ingrained in their attitudes towards spiders and schools are taking more initiative,” Whyte explained. “The mirror spider is so common around creek lines, especially in Brisbane. I can describe to a six-year-old ... and within five minutes they’ll go out looking for it.”
In fact, more and more people may have the chance to get on friendly terms with this marvelous miniature creature as the mirror spider’s habitat appears to be expanding.
Besides Australia, there are already several Thwaitesia in China and Vietnam, says Atkinson, and one species each in Myanmar and New Guinea. “I am confident that more Thwaitesia species will be found and described in Southeast Asia in the near future,” he added.
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