When danger threatens many lizards can detach their tails, leaving them behind as decoys in the hope that the predator will attack it rather than the lizard itself. But the tail doesn’t just lie there as bait. For half an hour after they’ve been severed, the disembodied tails perform a complex dance, flipping, lunging and jumping up to an inch in the air. These acrobatics serve to distract the predator even further.
For the first time, Timothy Higham and Anthony Russell have studied the movements of severed gecko tails to understand how they can move in such complex ways without any input from the animal’s brain. They anaesthetised four leopard geckos and implanted electrodes into their tails. Once the animals awoke, a small pinch in the right place was enough to prompt them to jettison their tails and scuttle for cover. As the tails started convulsing, Higham and Russell filmed them with high-speed cameras.
Their tips rapidly swung back and forth but between these rhythmic flexes, they behaved more erratically. They flipped by pushing the tip against the floor to launch the whole organ into the air and they lunged by doing the same, but horizontally.
These conspicuous movements increase the odds that an attacking predator will go for the tail instead of the lizard. But it’s actually in the lizard’s interests for both its body and its tail to escape being eaten – geckos and other lizards store valuable reserves of fat in their tails, and these are too valuable to leave to the jaws of another animal. As such, Higham and Russell think that the arrhythmic jumps and flips make the tail more unpredictable and harder to catch. They also increase the odds that the tail will flip to safety, say in a nook or crevice. The lizard can then return later to chow down on its ex-body part.
When sportsmen use rackets or bats, their best bet is to hit a ball on the “sweet spot”, the point where various forces balance out to deliver powerful blows with only very small forces on the wielder’s wrist. Engineers have the right tools and models to work out where this spot lies on their instruments. Now, palaeontologists have used the same techniques to study biological hammers that adorn the tails of giant prehistoric armadillos called glyptodonts.
At first glance, glyptodonts have little in common with the likes of Andy Murray and Roger Federer. These armoured beasts lived in the Americas several million years ago and the largest of them weighed up to two tons. Much like their modern armadillo relatives, they were clad in large suits of bony armour. Their long tails were similarly protected by bony rings and in some species, they were topped with large clubs, or spiky weapons that resembled medieval morning stars.
Uruguayan scientist Rudemar Ernesto Blanco was set about studying the tail clubs of the most formidable of the glyptodonts, by using the same approaches used to analyse sports tools. The analogy is particularly appropriate for species like Doedicurus, where the rings at the end of the tail were completely fused, meaning that the animal’s rear end was defended by a single metre-long piece of solid bone – a biological hammer, indeed.
When wielding this weapon, whether against a predator or a fellow glyptodont, it would be in the animal’s interest to strike at the sweet spot of its own tail to reduce the forces acting on the part of the tail where the bony tip met the more flexible base. Otherwise, it might have risked severe strain and damage. To find the locations of these spots, Blanco applied sports modelling techniques to the tails of nine species of glyptodonts.
It seems like an uneven match. In one corner, the unassuming California ground squirrel (Spermophilus beechyi), 30cm in length. In the other, the northern Pacific rattlesnake (Crotalus oreganos), more than twice the length of the squirrel, and armed with hinged fangs that pack a lethal venom. But thanks to a cunning adaptation, the squirrel often gets an unexpected upper hand in this bout.
Ground squirrels live in a series of burrows that keep them out of reach of most predators. Snakes, however, have exactly the right body plan for infiltrating long sinuous tunnels, and it’s not surprising that they are the squirrels’ major predators. It’s equally unsurprising that the squirrels have developed ways of defending themselves against snakes.
Adults have developed a certain degree of immunity to snake venom and their agility helps them avoid strikes. But their pups are still vulnerable and adults disguise their scents by chewing on the discarded skins of rattlers and licking them. When confronted, they harass the snake and wave about an upright tail. Among other benefits, this ‘tail-flagging’ tells the snake that it’s lost the element of surprise, alerts other squirrels and distracts the predator from vulnerable young.
But tail-flagging also has a hidden component that scientists have only just discovered. Aaron Rundus and colleagues from the University of California, Davis, found that the squirrels also heat up their upright tails, turning them into beacons of infrared light. It’s a countermeasure specifically evolved to exploit one of the rattlesnake’s deadliest abilities.
Geckos are nature’s champion climbers. With remarkable ease, they can scamper across ceilings and up smooth vertical surfaces, and they do so at speed. A vertically running gecko can cover 15 times the length of its body in a single second. So far, scientists have focused their attention on the gecko’s amazingly adhesive feet but a new study demonstrates the importance of a neglected piece of their climbing gear – their tails. Geckos use their tails to stop themselves from falling, and to land safely if they do.
A gecko’s foot is a marvel of biological engineering. Rather than relying on glues, suction or static, they stick to surfaces by exploiting ‘Van der Waals forces’, the weak forces that bind molecules together when they come in close proximity. Their technique was discovered a few years ago by researchers from the lab of Robert Full.
Each toe is covered in hundreds of thousands of tiny hairs called setae, and each of these is divided into up to a thousand smaller spatula-shaped hairs, just 200 nanometres long. When the gecko takes a step, these tiny hairs insinuate themselves into microscopic nooks and crannies so that even though the gecko has just five toes a foot, it’s effectively touching a surface in millions of different places.
The molecules of the setae become attracted to those of the surface and while these forces are individually very weak, their collective effect is strong enough to hold the gecko up. Nonetheless, even a gecko has its slippery moments and that’s when the tail comes into play.