Flattie spiders can sense prey approaching from any direction and whip around in a record-breaking one-eighth of a second to strike, new research has found.
High-speed footage reveals that a swift flex of their long legs helps the hunters accomplish this feat.
According to the researchers, their spin is the fastest leg-driven turning maneuver of any terrestrial animal, and also one of the fastest turns on the planet – on the same level as rapid airborne spinners such as hummingbirds and fruit flies.
The researchers are now modeling the spiders’ spins to help make multi-legged robots and other machines more maneuverable in tight spaces.
The study, conducted by researchers at the University of California Merced and the California Academy of Sciences involved using high-speed video cameras to document the movements of individuals from the Selenopidae spider family – commonly known as flattie spiders.
Flattie spiders can be found across North and South America as well as Africa, Asia and Australia.
Dr Crews, an expert on the Selenopidae family, searches field sites for cryptic individuals on trees and rocky surfaces – all in the dark – before bringing the nocturnal spiders back to the lab for study.
‘About half of all spiders species don’t use webs to catch prey,’ says Dr Sarah Crews, a postdoctoral researcher at the Academy.
‘Some stalk and pounce, while others are sit-and-wait ambushers – like flattie spiders.’
In order to document this rapid movement, which seems blurry to the naked eye, Dr Crews and lead author Dr Zeng of UC Merced set up two synchronized, highs-speed video cameras above and beside the spiders.
The team then examined strike footage at speeds about 40 times slower than the original to map the mechanics of this novel hunting maneuver.
‘We are documenting and modeling their fast spins to help chart a course for making robots and other machines more maneuverable,’ says Dr Zeng.
The ability of flattie spiders to spin rapidly lies in their legs: Their outward stance tracks parallel to the ground allowing for a wider range of unrestricted motion.
In addition, each leg faces a separate direction and as a result, covers a different portion of their 365-degree surroundings.
This means the spiders can spin to orient itself toward unsuspecting prey regardless of the angle of approach.
Flattie spiders have eight eyes, but researchers still do not know it any are actually used for seeing.
Instead, the spiders detect approaching prey, such as hopping crickets or buzzing fruit flies, via disturbances in the air current.
In order to stimulate the ambush of these sit-and-wait predators for each trial, the researchers released a cricket and allowed it to walk toward the spider, with the resulting strike footage of Selenops bifurcatus and Selenops insularis revealing surprising insights.
‘We found that the leg nearest the prey anchors to the ground, creating a leverage point from which the spider can pull in its torso closer to the prey,’ says Dr Zeng, describing the spider’s linear lunge.
Legs opposite the prey push off the ground to help.
Together, this combination of pull and push aprovides the beginnings of a twisting force – called torque – that propels the spider into a rapid spin.
Similarly to how figure skaters draw their arms inward to spin faster, flattie spiders pull their remaining legs in off the ground, holding them close.
This allows the spiders to spin up to 40 per cent faster and land perfectly positioned with their mouth towards their first bite of prey.
Around the world, flattie spiders are turning to strike their prey at speeds of up to 3,000 degrees per second.
In the time it takes you to blink your eyes, these spiders – when moving at full speed – can complete three full rotations.
‘Flattie spiders are always one step ahead in this evolutionary arms race between predator and prey,’ says Dr Crews.
‘If the prey are positioned further away, spiders move faster both linearly and with increasing rotational speeds – there’s truly no escape.’
While documenting spider spins has proven record-breaking, it also has practical applications.
‘Drawing inspiration from biodiversity like flattie spiders can lead to fascinating technological insights,’ says Zeng.
The team hopes their research on the mechanics of these rotations might inform the latest multi-legged robots and other machines required to maneuver in tight, confined spaces.
‘By simply observing these spiders and their natural history, we were able to make new discoveries across disciplines,’ says Dr Crews.
‘You just never know what path science may lead you down next – some of the best discoveries are made by accident.’