How One of the Fastest Spinning Animals Catches Its Prey

A paper detailing the hunting technique of flattie spiders could be used for developing multi-legged robots in the future.

Published 13 Feb 2018, 18:33 GMT
High-Speed Video Shows How Flattie Spiders Attack With World's Fastest Spin

If you blinked, you would have missed it.

Flattie spiders or wall crab spiders, which make up the Selenopidae family, have the fastest leg-driven turning manoeuvre of any land animal. Although their rapid turns are blurry to the naked eye, the crawlers are on par with the speeds of aerial spinners like hummingbirds and fruit flies. 

But now, researchers from the California Academy of Sciences and the University of California Merced are taking an in-depth look at these speedy spiders. By using slow-motion cameras, they've been able to identify how these animals can lunge for prey so quickly. Their findings, published February 12 in the Journal of Experimental Biology, could even provide insight for future robot design.

Speedy Science

Although known for their silk-spinning abilities, only about half of all spiders use webs to catch their prey. The other half rely on stalking and pouncing, while others, like the flattie spider, are speedy sit-and-wait ambushers. 

Flattie spiders have eight laterigrade, or sideways-moving, legs positioned at different angles to cover all 360 degrees of their bodies. This outward, ready-to-fire stance allows the spiders to spin. 

Sarah Crews, a postdoctoral researcher at the California Academy of Sciences, started the study by collecting Selenopidae spiders from trees and rocky surfaces. These nocturnal spiders are widespread, with 257 well-camouflaged species living in cracks and crevices throughout the Americas, Africa, Asia, and Australia.

Next, the researchers set up two synchronised, high-speed video cameras at angles above and beside the captured spiders. They then released one cricket at a time and recorded the spider quickly attacking it. Although flattie spiders have eight eyes—a row of six positioned on the front edge of the carapace and two large eyes on their posterior—it's unclear if they use these to see. Rather, the spiders detect prey by sensing disturbances in air currents.

Spider Vs Bee
Find out how a spider's eight eyes give it an advantage when hunting for prey. 

The researchers observed that flattie spiders anchor the leg closest to its prey firmly into the ground, creating a leverage point and torque for the spider. Then, pirouetting to face its meal, the spider will lunge mouth-first toward its target. At the same time, the spider will pull its remaining legs in toward its body. This allows the spider to spin 40 percent faster than it would with its legs extended, similar to how figure skaters spin faster when they pull their limbs in tight. (Related: "18 Spider-Killing Spiders Discovered—And They Look Like Pelicans")

This rapid hunting technique is something that has developed over time, the researchers say.

"Flattie spiders are always one step ahead in this evolutionary arms race between predator and prey," Crews says in a press release. "If the prey are positioned further away, spiders move faster both linearly and with increasing rotational speeds—there's truly no escape."

Pirouetting Predators

Flattie spiders can strike at speeds up to 3,000 degrees per second. That means that in the time it takes you to blink your eyes once, they can complete three full rotations.

The researchers say that the techniques that flattie spiders use to attack prey could be used in practical applications as well. For example, they could help guide the design of multi-legged robots to give the machines a wider range of movements. One bioinspired model already out there has a 3-D printed shell and eight spider-like legs containing individual motors to help the machine move. With this new research, future advances could give similar devices the ability to spin and change direction quickly. (Related: "These Tiny Scales Make Sharks Incredibly Fast. Can They Help Us Build Better Planes?")

"By simply observing these spiders and their natural history, we were able to make new discoveries across disciplines," Crews adds. "You just never know what path science may lead you down next."

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