Spider Masquerades as Bird Poo to Avoid Being Eaten

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One of the best ways to avoid being bothered is to masquerade as something unsavory, reports a new study identifying a spider whose web and body resemble bird droppings.

The orb-web Cyclosa ginnaga adds to the growing list of spiders that are nearly indistinguishable from avian excrement.

In this case, the spider sells the look via additions, otherwise known as "decorations," to its web, which may include carcasses, egg sacs, plant detritus or silk.

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Researchers Min-Hui Liu and colleagues explained: "We found that: (1) the presence of the spider's decorations rendered its body indistinguishable from bird droppings in the eyes of its predators and (2) concealing C. ginnaga's web decorations resulted in an increase in predatory attack probability. Accordingly, we concluded that the body and web decorations of C. ginnaga form a bird dropping masquerade to avoid predators."

Liu is a researcher at National Chung-Hsin University and the Taiwan Endemic Species Research Institute.

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.

At night, the spider engages in another form of mimicry. It releases a moth female sex pheromone that attracts male moths. Once the moths come close, the spider suddenly jumps into action, capturing the amorous moth victim with its powerful front legs.

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It's unclear if C. ginnaga enjoys such other benefits. What is clear is that these spiders, resemble bird feces in terms of color, size, and additional visual properties.

Take care in your garden! Things might not be all that they seem.

Photo: Arkys curtulus, aka "the bird-dropping spider." Credit: Peter Woodard, Wikimedia Commons

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