The southern beaches of Cumberland Island, off the coast of Georgia, USA, are part of a national park. To protect the area, only residents and staff are allowed to drive their vehicles on the sands. But there are plenty of wheels nonetheless – small, living ones.
The beaches are home to the beautiful coastal tiger beetle (Cicindela dorsalis media). Tiger beetles are among the fastest of insect runners, but their larvae are slow and worm-like. If they’re exposed and threatened, running isn’t an option. Instead, they turn themselves into living wheels. They leap into the air, coil their bodies into a loop, and hit the ground spinning. The wind carries them to safety.
The fact that a long, worm-like animal can jump and roll is amazing in its own right. The ability is even more remarkable because the tiger beetle is “one of the best-studied insect species in North America” and until a few years ago, no one had ever seen it doing this. Alan Harvey and Sarah Zukoff were the first. They write, “[Sarah] was walking through some unusually loose sandy drifts on Cumberland Island and happened to kick up some C. d. media larvae, which promptly started wheeling.”
To work out how they transform and roll out, the duo spent two summers looking for more burrows and flicking out the beetles with a well-placed trowel. If they prodded the exposed larvae with a blade of grass, the grub thrashed about the sand before suddenly zipping along its surface in a straight line.
That’s what it looks like to the human eye. High-speed cameras revealed more complex movements. Often, the beetle threatens its provocateur with its formidable jaws (see right). Sometimes, it plays dead or throws up.
If you touch it on its bottom half, it arches its body backwards head-to-tail, forming a loop. It then violently uncoils, launching itself off the sand and coiling in the other direction. When it hits the again, its momentum carries it forward. It can also land in the right direction to roll with the wind. Its mad thrashing is really its way of turning its ignition and steering.
Once started, the beetles continue rolling in the direction of the wind. They move at around one mile per hour, spinning at 20 to 30 revs per second, and travelling for up to 25 metres. If the winds are particularly strong, they could roll faster than Harvey and Zukoff’s assistant could run – around 7 miles per hour on the sand.
They hold their three pairs of legs out to the side to balance (the videos showed them wobbling but not falling over). And they’re strangely manoeuvrable – by pushing off with their tails, they can do jumps mid-roll to gain extra speed, and even change direction by 90 degrees.
In Phillip Pullman’s His Dark Materials trilogy, fantasy creatures call mulefa roll around by sticking their legs through the holes of large, round seeds. In the real world, there are no animals whose bodies include proper wheels, which turn about an axle. Stephen Jay Gould famously argued that such adaptations would be impossible. The wheel would need to rotate freely about the axle, so if they were both part of the same individual, how would it carry nutrients or nervous signals to the wheel?
Nonetheless, animals can turn their entire bodies into rudimentary rolling wheels, albeit without the accompanying axles. Many species have independently reinvented the wheel technique. The wheel spider (or dancing white lady spider) cartwheels down the dunes of Africa’s Namib Desert by flipping on its side, and tucking its legs in to form spokes. It also rolls defensively, to escape from body-snatching wasps. One species of salamander, the pearl moth caterpillar, and one species of mantis shrimp can all do the same.
Some of these species use gravity to power their rolls. But uniquely, the tiger beetle usually rolls uphill. It relies on the wind to push it along and during the day when it’s most active, the prevailing winds usually blow up the beach form the ocean. It’s a fair bet that they don’t use the same technique at night, when they would just blow out to sea.
Once they get going, the only thing that foils the beetles’ wild rides is a rough beach. Rocks, ridges and uneven patches of sand can stop them in their tracks. Sadly, these features are becoming more and more common as Cumberland Island’s beaches are trampled by 40,000 tourists a year. Perhaps this explains why the beetle’s populations have recently plummeted across American beaches, particularly heavily used ones. Where humans are on a roll, the beetles aren’t.
Reference: Harvey, A., & Zukoff, S. (2011). Wind-Powered Wheel Locomotion, Initiated by Leaping Somersaults, in Larvae of the Southeastern Beach Tiger Beetle (Cicindela dorsalis media) PLoS ONE, 6 (3) DOI: 10.1371/journal.pone.0017746
Photos: Adult tiger beetle by Sean McCann, larva by Antony Zukoff
More on animal movements:
- Pocket Science – belly-flopping frogs, and fattening marmots
- Scientists solve millennia-old mystery about the argonaut octopus
- Caterpillars must walk before they can anally scrape
- Fossil tracks show a pterosaur coming in for a landing
- Swimming, walking salamander robot reconstructs invasion of land
- Funky gibbons
- Running dragon lizards do wheelies
- Anna’s hummingbird outflies falcons and fighter pilots
March 25th, 2011 at 10:56 am
Can’t post about rolling without Rick, huh? Nicely done.
As always, a great read.
March 25th, 2011 at 11:09 am
They see me rollin’, they hatin’….
March 25th, 2011 at 11:24 am
Very much like the Curl-up (Pedalternorotandomovens centroculatus articulosus) of M. C. Escher. Must be convergent evolution.
See the Wickipedia article “Curl-up”.
March 25th, 2011 at 12:34 pm
Nice Move…! turn into an ant robot ….good for spying mission.
March 25th, 2011 at 1:30 pm
Wow. Time to rock and/or roll.
March 25th, 2011 at 4:26 pm
So, animals actually invented the wheel, way before we did it.
March 26th, 2011 at 2:56 am
Hang on !
Invented the wheel?
What about the irreducibly complex flagellum?
March 26th, 2011 at 3:49 am
There’s also a rolling toad: http://www.youtube.com/watch?v=tOmbooEY4x4
March 26th, 2011 at 11:37 am
“Sadly, these features are becoming more and more common as Cumberland Island’s beaches are trampled by 40,000 tourists a year.”
More common? Doesn’t sound right.
March 26th, 2011 at 12:39 pm
Re: rolling white spider. I thought the music they were playing was White and Nerdy (Weird Al’s spoof of Riding Dirty)…it seemed to fit at the time.
March 26th, 2011 at 12:40 pm
I just wanted to let you know that posting this article on Reddit got me on the front page (for those who track science posts) for the first time ever!
So thanks for that. : ) Great read, great videos, and super groan-worthy puns.
March 26th, 2011 at 3:23 pm
I wonder if these animals feel really, really dizzy when they’re through rolling.
March 26th, 2011 at 3:51 pm
I would like to see one of these beetle larvae chased by a Saharan rolling spider (Araneus rota) -
http://tywkiwdbi.blogspot.com/2009/04/saharan-rolling-spider-araneus-rota.html
March 26th, 2011 at 5:21 pm
@Robert S-R – And many thanks for the traffic boost. Yeah, I may have perhaps gone overboard on the puns, but I was on a ro… OH STOP.
March 26th, 2011 at 5:38 pm
If you like tiger beetles, you might like this project, too: “Meet the Beetle” will tell the story of the Salt Creek Tiger Beetle, one of the rarest insects in the world.
http://www.kickstarter.com/projects/209123822/meet-the-beetle-a-film-about-the-rarest-insect-in
March 27th, 2011 at 11:54 am
@Albertonykus – I remembered the pebble toad, but I don’t really think it counts. It’s not so much a wheel as a ball, not quite rolling but (to quote Buzz Lightyear) “falling with style”.
March 27th, 2011 at 6:47 pm
Wow, is that jsut cool or what? Amazing.
http://www.privacy-online.it.tc
March 28th, 2011 at 6:52 am
FYI: “blow up the beach form the ocean” -> “blow up the beach from the ocean”
Great blog, thanks!
March 29th, 2011 at 5:31 pm
There are several Cicindela species that run along the beaches. Did the authors rear the larvae to adulthood to make certain of their identifica-tion, or did they just make an assumption? It is likely that the behavior is generalized, rather than species-specific, but it would make better science to be certain of the species being quoted in the title.
April 4th, 2011 at 9:58 am
Very very cool article and a fun read with the embedded videos. Thanks!
April 13th, 2011 at 5:11 pm
“I can’t tell you how I feel
My larva’s like a wheel
Let me roll it”
~~Paul McCartney (Beatle)