Looking to start a family? Bust a move

Some animals get only one chance to find a mate—and there’s a lot riding on their ability to perform.

Written by       Illustrated by Giselle Clarkson

Giselle Clarkson

When they’re looking for a mate, many animals seem to dance. Blue-footed boobies lift their turquoise feet in turn, nod their heads, then stretch out their wings and gaze upwards—a manoeuvre dubbed “sky-pointing”. Male sage-grouses on North America’s Great Plains favour a kind of body-popping—thrusting their chests forwards to fling out their bulbous, colourful air-sacs, which make a rhythmic, watery, two-toned sound that travels for up to three kilometres.

Flamingos, meanwhile, strut and high-step in unison, or tiptoe back and forth in synchronised groups, their gangly yellow legs appearing to move as one as they side-eye each other to see who has the best moves. Male birds of paradise inflate their plumage and seem to shape-shift into entirely new animals—becoming a bouncing, iridescent monster, or a spinning black ball of feathers, before flipping their head from side to side as though grooving to a beat only they can hear.

Seahorses entwine tenderly like contemporary dancers, while other animals’ manoeuvres seem to have more in common with capoeira, an Afro-Brazilian martial art disguised as a dance. In the rivers of India’s Western Ghats, male small torrent frogs threaten their rivals by showing a little leg, or “foot-flagging”—a crouched shudder, a graceful extension, a pause in the splits, then back to neutral with a snap of the thigh.

Spiders take the concept of the mating dance to the next level. Male peacock spiders raise their psychedelic, iridescent bums in the air, side-step and shimmy, and wave their third set of legs. It’s musical as well as visual—the spiders vibrate whatever they’re standing on in percussive manoeuvres scientists have dubbed “rumble-rumps”, “crunch-rolls”, and “grind-revs”. There are more than 100 species of peacock spider, all found in Australia, and each one has a uniquely coloured and patterned butt-flap and its own sequence of dance moves. A perfect-10 performance and a male will be rewarded with a mate; if he fails to put in enough effort, or his leg-waving does not meet the female’s standards, she might attack him.

There’s even more dancing diversity among wolf spiders—an enormous family of arachnids containing more than 2000 species. Eileen Hebets from the University of Nebraska-Lincoln in the United States studies the Schizocosa genus in the lab, trying to find out why spiders put so much effort into dancing and percussion. “Each one’s dance is totally different, which is part of the fun. When you get a new species, it’s like a whole new discovery—like, what’s this one gonna do?”

Getting the males to bust their moves is ridiculously easy. All Hebets has to do is place a female wolf spider on a piece of filter paper for half an hour. As the spider walks around, she leaves traces of pheromone-soaked silk behind on the paper. Hebets removes the female and puts a male in her place. “He’ll start chemo-exploring and picking up chemicals from her presence. And that’s enough to really start him going crazy with his courtship.”

The female spider isn’t even there any more—only the chemicals she’s left behind—but the male puts his whole body into his performance. He might wave his beautifully patterned or intensely hairy legs in the air, drum his pedipalps—his pincers—on the table, vibrate his muscles, or scrape one pincer against the ridges of the other as though drawing a knife along a comb. He could even throw his entire body to the floor like a breakdancer.

“Some of them are so vigorous that when they hit the ground, you can hear it,” says Hebets. Usually, though, the scientists need to use a laser to convert the vibrations to audio so they can listen to them. Each type of wolf spider has its signature sound: “You can tell just by listening what species it is.”

For minutes, even hours, the male wolf spider dances like no one’s watching. (Unfortunately for him, no one is, except for a few scientists.)

Males are born knowing these routines. They don’t learn them, or make up their own steps—but they’re not automated, either. Hebets has discovered that some males adjust their performances based on feedback from the watching female.

In a few Schizocosa species, females mate only once in their lives. “They only get one shot, so it’s a really big decision,” Hebets says.

So how does a female wolf spider choose? She looks for the dancer with the most intricate moves. Hebets’ team found that the more complex a male’s dance—the more different the moves, the greater combination of visual and sound elements—the more likely it is that a female will decide to mate with him.

Scientists still aren’t sure why that is, but they have a few theories. “Like, the coordination that it takes to do very elaborate things in some way speaks to his skill and ability,” says Hebets—and therefore his genetic fitness.

It’s also possible that the more intricate dances are somehow more aesthetically pleasing to the females—that their brains are wired for the complexity of the wild, and watching and listening to a lively and detailed display is therefore a better experience than sitting through a ho-hum one.

Some elements, like the hairy leg-brushes, seem to help males to impress females only in low light. “It may not be as obvious as ‘All females like hairy legs all the time’,” says Hebets. “Females are not all the same. They’re individuals, they have individual experiences, they change throughout their lives. Even spiders.”

Overall, Hebets hopes these dancing spiders will help to answer the big question of why animal communication is so diverse, and sometimes so elaborate. Why don’t all spiders do the same thing? Why do they put so much energy into these displays? How does the combination of sound and vision—the drumming and the dancing—get paired and processed in the spider’s brain? “Wolf spiders are a system where we can pull all of that apart and ask all these questions.”

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