For the study, published in the latest issue of Scientific Reports, Liu and the other scientists compared the spider's body and its web to bird poop, in terms of how they reflect light and otherwise appear in a natural setting.
Since those values were so similar, the scientists suspected that wasp predators could not distinguish between these very different items. They tested the theory by monitoring what happened when they blackened, with carbon powder, some of the spider bodies, thus ridding the spiders of their disguise.
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Sure enough, the blackened spiders were quickly attacked and eaten by the wasps. The other spiders, retaining their poop look, were usually ignored.
Masquerading as bird poo could be much more common than previously thought among spiders. The spider Celaenia excavate's common name is "the bird-dropping spider." Species from the genus Mastophora, such as the bolas spider, also resemble bird feces.
In addition to keeping predators at bay, the disguise may help the spiders to fool their own prey. The bird-dropping spider, for example, stays motionless on its web during the day to fool passers by.