Animals have evolved lots of creative ways to blend in with their environments, developing colors or body types that help them hide from predators. But sometimes, camouflage isn’t enough, and a creature has to masquerade as something else. Some creatures pretend to be an object that no animal would want to eat — like twig caterpillars, which try to outwit birds by looking like sticks.
Juvenile orb weaver spiders have another great trick: They make themselves look like big white splats of bird poop. Predators, which include wasps and ants, are thus less interested in snacking on them.
Min-Hui Liu and colleagues looked at some orb-webs spun by a species called Cyclosa ginnaga, and noticed they contain a white disc-shaped silk “decoration.” With a silvery spider hanging out in the middle and brown spotted legs sticking out the sides, the dotted white disc looks like bird droppings. It’s even the same size as an average bird splat. The team hypothesized that this was not an accident.
The researchers measured the reflectance of the spider, the white decoration, and bird droppings in a natural setting. They found the real bird poo and the bird poo costume were indistinguishable, as viewed by the spiders’ insect predators.
Just to be sure, they sprinkled black powder on the white decorations of some orb weavers, creating a much greater color contrast. They also sprinkled powder on webs and spiders, to measure what happened. Then they turned on some video cameras to capture 197 hours, 132 hours, 122 hours and 119 hours of footage.
As they expected, spiders with blacked-out decorations but not blacked-out bodies were more likely to be attacked by wasps. So masquerading as bird poo is an effective way to fool your enemies, the researchers suggest. But they still have to show that wasps repeatedly mistook C. ginnaga costumes as bird droppings, they add.
“Further observations of wasp responses to bird dropping are, therefore, required before masquerading can be definitively concluded,” they write.
Their paper appears in Nature Scientific Reports.