This Spider Attracts Its Prey By Acting Like Bird Poop

It almost sounds like a game procession: You look like bird poop and smell like it.

For the aptly named bird dung crab spiders that live in the tropical rainforests of Southeast Asia, such looks and smells are crucial to survival in a world where they are eaten or eaten.

“All spiders are predators, but they also have their own predators,” he said. Daiqin Li, a biologist at the National University of Singapore. Spiders’ shiny black-and-white patterns and foul odor are part of a mephitic mask that deceives predators who would otherwise try to eat the spiders – after all, birds tend to avoid swallowing what they’ve already completely digested.

But the imitation of bird dung spiders serves another role.

According to a study published last month Current ZoologyThe spider’s faeces attract prey while repelling predators—the first masked species described to use what researchers call aggressive mimicry to actively lure it at lunch.

Previous research had hypothesized that the masquerade of crab spiders could attract unfortunate insects. But until now, no one had experimental evidence. Still, the idea made sense because for many insect species, bird droppings are both attractive food sources and inviting homes to lay their eggs. Crab spiders are also sit-and-wait hunters, preferring to ambush unsuspecting prey that lands on their leaves.

Dr. “They stay there for more than 12 hours,” Li said. “Sometimes they stay there for the rest of their lives.”

To test the hypothesis, the researchers first videotaped the spiders as they sit on leaves in the wild, and then compared the ensuing swarms of insects with those captured by similar-sized bird droppings. (Dr. Li notes that they need to make sure the droppings are “wet enough” because dry droppings don’t attract many insects.)

Insects visited both spiders and bird droppings at significantly higher rates than empty leaves. Although spiders attracted insects, especially flies, real feces attracted them at a higher rate.

Next, to test whether the spiders’ signature color combination was the key to fooling some insects, the researchers applied an odorless watercolor paint to manipulate the spiders’ colors. Spiders that were painted all-white or all-black were less attractive to insects than unpainted spiders or those dyed the color they were already, so looking like bird droppings was key to deception. (When the researchers finished observing the spiders, the paint was easily washed away by the drops of water.)

The researchers also modeled what the insects would see in their visual systems and found that unlucky prey might not be able to discern the difference between a hungry spider and real bird droppings.

Not that we humans can do much better.

“Many people can’t even tell the spider from bird to bird,” he said. Stano PekarA zoologist from Masaryk University in the Czech Republic, who was not involved in the study, said his results were impressive. “I mean, they have a really good masquerade ball.”

The findings have opened up new questions about how the fertilizer scam evolves. Dr. Other crab spider species have different patterns and proportions of white and black on their bodies, which could affect how convincing they are for insects, Li said. (The more “typical” types of crab spider are green and white, allowing them to blend into the leaves; they also don’t smell like bird droppings and attract much less flies.)

Other animals have also evolved to mask themselves as inedible or inanimate objects to protect themselves from predators – the larvae of early thorn moths look like twigs, and butterflies with dead leaves look like dead leaves. But researchers rarely investigate whether coloring tricks can serve more than one function of the same type. That could change, said Dr. pekar.

“I think in the future,” he said, “we will see many more cases where both the color and the pattern will be both defensive and offensive.”