Geckos gather upside down on my balcony ceiling at night, watching insects swarm a lamp. Their ability to defy gravity mystified scientists for years. Many searched for the elusive glue, or the gecko’s answer to spider silk, but it was all in vain as the stealthy killers left no footprint where they walked.
This single-minded predator makes itself practically invisible during a hunt by locking its body and limbs down to perfect stillness. The only movement while it watches is a flick of the tongue to moisten vertically slit eyeballs, wired for night-vision by the relentless attrition of evolution.
There is no escape from the final lightening strike. In a split-second two or three insect legs bicycle uselessly out of the gecko’s stuffed mouth, half a wing trembles. They'll eat all sorts of small animals, but their favourite are the winged insects. The predator chews its prey to death, mashing them up with sharp teeth.
In any Hong Kong apartment it could be a Bowring’s gecko, or a four-clawed gecko with purple and peach skin stretched almost translucent over a potbelly full of dead bugs. You can hear their devilish clicks at night. They are the only reptiles with vocal chords. Like chameleons they can adjust skin colour for camouflage, though their range is restricted to tone, light to dark.
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| Four-clawed gecko. Source: AFCD |
Eight different species reside in Hong Kong. In addition to the common Bowring's and four-clawed geckos, there are large biters like the Chinese and the tokay, warty spike-tailed specimens in the Brook’s, and a shy forest dweller in the tree gecko. The house gecko, on the other hand, loves to hang out in our homes, and inside our stuff, especially electrical gear like air conditioners, toasters and at the back of the fridge.
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| Chinese gecko. Source: AFCD |
Some are regional such as the Chinese gecko limited to central and southern China and northern Vietnam, while others are far travellers like Brook’s that spread across Asia and also appear in the West Indies and tropical Africa.
The tokay, reaching 40 cm in length, is the second largest gecko in the world, beaten for size only by the New Caledonian giant gecko. Named after their distinctive "To-kay" calls, these blue-skinned, red-spotted carnivores are our most aggressive species. Males will fight each other for a mate, but they’ll make peace for long enough to hunt in packs. They are known to attack small mammals and birds, and they will bite a human finger if given half a chance.
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| Tokay gecko: AFCD |
But these dragons-in-miniature have much more to fear from us than we have of them. Wanted dead or alive, tokay geckos are hot items in both the global pet trade and the Chinese medicine market.
Hong Kong's "native" tokays, sometimes spotted on Lantau island and around Lion Rock, are thought to be mostly the decendents of drug-trade escapees. And in urban areas we are more likely to see them dead and splayed flat like small grizzly kites outside a snake shop, than surviving unmolested in some crack in an old wall. In the old quarters of Hong Kong, such as Shueng Wan, you can see hundreds of these gecko lollipops on their bamboo crucifixes.
As with much of Chinese medicine it is difficult to pin down a convincing description of how ingesting an exotic species can have health benefits. But medicine shops list a diverse range of benefits brought by the tokay from “replenishing the lungs and kidneys” to “receive qi and stop asthma” and “reinforcing yang and essence.” It is also indicated for pulmonary tuberculosis, impotence and “seminal emission,” quite a potpourri of unrelated complaints.
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| Credit: Krishna, Public Domain Photos |
Whether for medicine or the huge global pet trade, there is a long history of trapping, eating, breeding these geckos, and as a result the tokay is endangered in China, and ironically, a protected species.
But however tentatively, several other gecko species live well on the peripheries of the built environment, hunting, sheltering and breeding inside things made by people.
Female geckos typically lay two eggs at a time, a few times a year. Whether a gecko lays eggs inside apartments, on the eaves of a pagoda or beneath a park bench, the main thing is that the eggs are kept out of the rain. I've discovered them attached to my disused spare shower wall, lodged behind a water pipe. They were perfect little eggs, slightly squashed balls of shiny and speckled ivory.
I inadvertently destroyed another batch when I pulled out a long redundant plastic poncho from a basket hanging on a wall. Three eggs dropped and two of them smashed to reveal miniature gecko forms, one of them was alive but it didn't last long. The shell of the third egg cracked and fell away, revealing a tightly packed ball of baby gecko inside a soft sack. I carefully placed it in a plant pot in the hope that it would hatch, but the the little lizard never woke up.
When geckos don't have the convenience of the facilities humans have built, they resort to tree crevices under a canopy of leaves to lay eggs, an old world they knew for millions of years before we discovered bricks, mortar, metal and glass.
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| A self-cloning Garnots's gecko |
Geckos generally follow the usual practices of sexual reproduction, popular with most animals, but one Hong Kong species has dispensed with sex altogether. The Garnot’s gecko practices the strange art of parthenogenesis – self-cloning. All of them are females, with no use for males, as their eggs develop into embryos without the help of fertilisation – an exact copy of the mother, who is also an exact copy of her mother, give or take a few random mutations.
While examples of self-cloning can be found quite frequently in plants and simple invertebrates, it’s reckoned that there are only a few dozen vertebrate species that practice asexuality.
Some biologists believe that parthenogenisis is a great idea. If a parent has lived long enough to produce viable eggs, she has obviously got perfectly good genes. Why change anything by introducing the DNA of a random stranger? Considering how hard relationships are to manage, the parthenogenic lizards such as Garnot’s geckos may have chosen an unusual but perfectly reasonable method to reproduce. But strangely enough this biological choice hasn’t necessarily let them escape the trials and tribulations of courtship and relationship after all.
Not if a lizard study published in 1979 has implications on Garnot’s anyway. In this account self-replicating reptiles still have to pair up and go through the motions as lovers, to kick their hormones into action and set the reproductive process off.
Other than the rare and mysterious self-cloning powers of Garnot’s, geckos in general have evolved into biological machines of wonder, avidly studied today in the hope that they will unlock superhuman powers. There are two traits in particular that interest powerful and sometimes shadowy institutions, their ability to stick to walls and ceilings, and their ability to re-grow their tails.
Their powers of adhesion are amongst the best in the natural world, with an intriguing clamp and peel mechanism on their foot pads that offers potentials in robotics such as wall-climbing spy-bots of future warfare, or even bionic prosthetics for tomorrow’s special agents. Until recently many biologists believed that these agile stalkers used some kind of secretion to stick to walls, like spiders with their silk, but now we know better. Less than two decades ago scientists proved that submolecular electrical forces of attraction -- called Van der Waal's supplemented the gecko's otherwise ordinary use of claws and friction.
The same forces of attraction that keep molecules together, from gasses to liquids and solids, keeps a gecko stuck to your wall.
Their claws naturally play a part in finding a toe-hold on surfaces, but millions of tiny hairs called lamellae cover the toes and foot pads, and each of these splay into billions of nanoscale split-ends called spatulae. This multiplies the total surface area of gecko foot in actual contact with any wall or ceiling by a huge factor. In contrast, when we put a bare foot on the ground, at a microscopic level there are huge gaps between our skin and the surface it it is touching. We think we are making firm contact, but in reality we are balancing on a rough terrain of invisible ridges and pin points. In the case of geckos, all the tiny nanoscale holes are filled up by billions of microscopic hairs. This allows Van der Waal’s forces to interact with surface molecules to make a bond strong enough to suspend the body weight a gecko from a ceiling.
But that’s just half the story. The other half is letting go. Stealth and speed are vital to the gecko’s survival strategy, contributing to the 100-million-year durability of their basic body design. That means adhesion must be backed up by split-second release.
It’s all in the subtle directional pull applied by the muscles. A gecko can hang on glass by one toe, if it pulls it back, according to researchers at Stanford University. They explained that its sticking-power only works when there is a force pulling in a certain direction, described as a kind of “one-way adhesive.”
The team created an adhesive that mimics the lizard’s directional bonding system, made up of a rubber-like material with polymer threads a fifth of the thickness of a human hair.
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| Credit: IB.Berkeley.edu |
They spent years creating a prototype robot dubbed Stickybot that can scale up smooth glass surfaces. Its form even resembles a lizard, with four limbs and a tail, and it is hoped that eventually its descendants will be doing real practical work for human masters, by reaching dangerous and tricky places.
Another line in development is a scaled up version of the system for grown-up human use. They call the technology Z-Man, and one appeared in a demonstration in 2014. A 98kg man climbed up 8 metres of smooth glass carrying a 20kg backpack. His only climbing aids were a pair of paddles lined with an adhesive inspired by gecko skin. His well publicised antics triggered a slew of awkward headlines around the world where Spiderman references were deemed essential to explain the gecko-inspired technology.
But what was it for?
“The gecko is one of the champion climbers in the animal kingdom,” said Dr Matt Goodman, one of scientists working on the project. “So it was natural for DARPA to look to it for inspiration in overcoming some of the maneuver challenges that US forces face in urban environments.”
So what is this mysterious DARPA? It’s got a darkly Orwellian name and it pays grown men to goof around all day dreaming of soldiers in giant gecko suits.
The Defense Advanced Research Projects Agency came in to being in 1957 after the United States was caught flatfooted by the communist Soviet Union when it launched Sputnik into space, the world’s first communications satellite.
The new agency, set up to ensure America would never again be caught by surprise, went on to help invent the F-117 stealth fighter, which dropped 2,000 tons of bombs in the 1991 Desert Storm campaign to oust Iraq’s Saddam Hussein from Kuwait. It also invented the M-16 assault rifle, the US army’s shoulder weapon of choice. But DARPA’s most ubiquitous invention was the Internet, which came about when the agency sought ways to link up computers between researchers spread across the United States. No one can doubt the enormous influence the Internet has had on the world since it spilled out of DARPA’s secretive world and ignited a communications revolution.
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