Blink and you might miss it: a thorny devil eating its lunch is just too fast. Jay Meyers from Northern Arizona University is intrigued by the speedy eating habits of these spiky ant-eating lizards. To find out exactly how the specialist feeders catch their prey, Meyers teamed up with Anthony Herrel of the University of Antwerp to film lizards grabbing their grub(p. 113).
Meyers explains that the thorny devil has to eat a lot of ants to get a square meal, since the tiny insects are not very nutritious. Thorny devils need to eat about 2000 ants a day to stay alive, but catching such large numbers of small prey is incredibly time-consuming. Lizards that do not specialize in ant-eating are slow eaters. If these non-specialists were forced to feast on ants only, given their average prey capture speed, they would have to spend eight hours a day chomping ants to survive. Clearly this leaves no time for other essential activities like mating and sleeping, so ant-eating specialists like the thorny devil need to eat fast. But how do specialist lizards manage to eat faster than other species? Meyers and Herrel decided to compare high-speed video recordings of two ant-eating specialists, the Australian thorny devil and the North American horned lizard, with those of two species that only occasionally eat ants, the Australian bearded dragon and the North American fringe-toed lizard.
Scampering around Arizona's sand dunes to catch the North American species was straightforward enough. Then Meyers and Herrel flew to Australia for a conference, planning to extend their stay to film thorny devils. But here they hit a snag. `We drove for 10,000 miles and only managed to find one devil'Meyers recalls. Discouraged, and with little else to do in the middle of the desert, the pair visited a reptile centre in Alice Springs to raise their spirits. To their astonishment, they found ten thorny devils munching away on ants. Luckily the centre's owner was happy to help and allowed them to film the spiky creatures. `We set up a high-speed camera in the lizards' enclosure,set a column of ants marching towards the camera, and collected our data in just a few days' says Meyers.
Back in Arizona, the team began analysing the videos. Using seven anatomical landmarks around the reptiles' mouths as x and yco-ordinates on each frame, they were able to time 27 kinematic variables,such as the duration of mouth opening, tongue movement and prey processing.`It was immediately obvious that the anteating specialists were eating faster than the non-specialist lizards' says Meyers, `but most noticeable was that the thorny devils' behaviour was strikingly different from the other three species.' He explains that lizard feeding behaviour normally begins with a slow mouth-opening phase during which the animal languidly decides whether to eat its prey. But when the team looked at the lizards' kinematic profiles,they saw that the thorny devil completely skips this traditional slow mouth-opening phase. It opens its mouth quickly and flicks its tongue out to catch its hapless prey. Even more surprising is that thorny devils barely process their prey; they don't chew their food but swallow it whole. `Thorny devils have simply modified their behaviour' says Meyers, `they are not doing anything clever physiologically that other lizards wouldn't be able to do.'
So the secret of the ant-specialists' success is bad table manners; they open their mouths quickly to snatch their food and they swallow without chewing. Meyers calculates that, thanks to their superfast feeding, thorny devils can meet their energy requirements by eating for just two hours a day. Clearly, these are no lounge lizards.