Makeup fails to solve mystery of why jumping spiders have back stripes

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Researchers have come up with an ingenious way to test the theory that male jumping spiders have evolved colourful stripes to ward off predators – they have put makeup on them.

Unlike the females of the species, the male Habronattus pyrrithrix come in vivid hues to attract mates. But scientists writing in the journal Royal Society Open Science wanted to establish whether their bright, striped backs help protect them from predators.

“In the field, when a male sees a female, he just kind of ignores his surroundings … they’re just so focused on the female that they’re not really paying attention to what’s going on behind them. So, it made us think that maybe they need some extra protection from things eating them,” said study author Dr Lisa Taylor from the University of Florida.

The researchers used makeup to paint the backs of both male and female spiders – in an effort to make each sex look like the opposite to assess whether that would change the behaviour of a key predator: the substantially larger jumping spider, Phidippus californicus.

With the assistance of a microscope, Taylor said the males had their back stripes dimmed using foundation powder – while Urban Decay’s black liquid eyeliner was used to draw bold black stripes on the back of the females.

“I had never really thought as much about makeup until I started studying spiders, but when you apply the makeup … and you can see how cleanly and how finely it goes on – it’s not quite as intricate as like painting a grain of rice, but sometimes it feels that way,” she said.

Although the researchers expected the males’ bright back pattern combined with behaviour that appears to mimic insects like wasps and bees would help them avoid predators, instead they found that having a striped shell increased the likelihood they would be attacked.

They also found that males, regardless of whether they had their natural colour or had makeup applied to them – were just more likely to be captured, Taylor said. “So, it seemed like, at least with this particular predator, the colour patterns didn’t really matter.”

Overall, the question about why these male jumping spiders have colourful backs still hasn’t been answered, the researchers wrote.

But the next most likely explanation is that the stripes do not help the males against the predator used in this study, said Taylor. “But I still think it would help the males against a different type of predator,” she said.

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