The wing of a fruit fly, viewed against a white background, looks very ordinary. It is transparent, with no obvious colours except for some small brownish spots. But looks can be deceptive. If you put the wing in front of a black background, it suddenly explodes in a kaleidoscope of colour. Oranges, blues, greens, violets – virtually the entire rainbow dances across the wing, except for red.
A French scientist called Claude Charles Goureau first noticed these vivid hues back in 1843. Since then, they have languished in obscurity, “apparently unnoticed by contemporary biologists”. Whenever new species of wasps or flies are described, their discoverers almost never mention the coloured patterns of the wings. The visible pigments have even been described as “evolution in black and white”. It’s like walking through an art gallery with a blindfold.
Now, Ekaterina Shevtsova from Lund University has taken off the blind. By photographing several species against dark backgrounds, she has revealed a world of hidden colour, rivalling that of more obviously beautiful insects. “The claim that fly and wasp wing patterns are no match for the incredible diversity of colourful butterfly wing patterns is obsolete,” she says.
In a small forest clearing in Papua New Guinea, a male six-wired bird of paradise is getting ready for a show-stopping number. He rears up and spreads his wings so that they encircle his body like a ballerina’s skirt. He begins to dance, bobbing from side to side to side while shaking his head and waggling his six bizarre plumed wires. And all the while, his chest feathers flash with an ever-changing palette of orange, yellow, green and blue. Few animal displays so wonderfully merge the sublime and the ridiculous.
The flashing chest feathers are an eye-catching part of the bird’s routine. Many birds, from peacocks to starlings, have shiny feathers that change colour but those belonging to the six-wired bird of paradise are special. Thanks to their unique shape, each one acts as a three-way mirror, allowing the bird to produce changes of colour that are far more dramatic than what other birds can manage.
This is an arachnophobe’s worst nightmare: the largest spider web in the world. It belongs to the Darwin’s bark spider, which spins its gargantuan trap over entire rivers and lakes. Its shape – a simple ‘orb web’ – is normal enough, but its size is anything but. The main anchor thread that holds the web in place to both riverbanks can be as long as 25 metres and the main sticky core can be as large as 2.8 square metres.
With a web that big, it’s no surprise that Darwin’s bark spider uses the toughest silk of any species. It can resist twice as much force as any other spider silk before rupturing, and over 10 times more than a similarly sized piece of Kevlar. It’s not just the apex of spider silk – it’s the toughest biological material ever found.
Not Exactly Pocket Science is a set of shorter write-ups on new stories with links to more detailed takes by the world’s best journalists and bloggers. It is meant to complement the usual fare of detailed pieces that are typical for this blog.
Bursting bubbles create rings of daughter bubbles
Popping a bubble on a body of water seems like an unspectacular event, but there’s real beauty in what happens if you look at it carefully. For James Bird at Harvard University, that meant filming the exploding bubbles with a high-speed camera. His beautiful videos reveal that contrary to popular belief, a popped bubble doesn’t just vanish. Instead, it gives birth to a ring of smaller daughter bubbles, each of which can produce an even smaller ring when it bursts.
The bubble’s curved nature means that the air inside it is at a higher pressure than air outside it. When a hole forms in the bubble, this pressure difference disappears and the film starts to recedes away. The film experiences an inward force along its surface, but an outward force at its rim – as a result, it folds outwards back onto itself, trapping a donut of air. The donut, however, is unstable and it soon breaks up into several smaller bubbles. The whole process takes place in a few thousandths of a second and it can only happen twice before the daughter bubbles get too small.
This process is surprisingly common. It applies to liquids from water to oil, regardless of their viscosity, and it happens in soapy sinks and foamy oceans alike. Bird also found that the bursting of each daughter bubble released tiny liquid droplets into the atmosphere. These aerosols may be miniscule but they have a few important repercussions. They’ve been implicated in the spread of infectious diseases in swimming pools and hot tubs and they contribute to the cycling of chemicals from the oceans into the atmosphere.
Reference: Nature http://dx.doi.org/10.1038/nature09069
More from Geoff Brumfiel at Nature
Image and video by C.Bird
Snakes on the wane (credit to Sciencepunk for the headline)
A depressing number of important animal groups are facing massive population crashes, including amphibians, corals and most recently lizards. Now snakes are the latest faction to join this pessimistic list. An international team of scientists led by CJ Reading did a survey of 17 snake populations, covering 8 species from the European grass snake to the African gaboon viper. They found that 11 of the populations have declined at an alarming rate since the mid 1990s, while 5 have remained relatively stable. The crashing populations all showed a “tipping point” trend, where their numbers suddenly and steeply fell over four years, after a lengthy period of stability. They’ve all levelled off since but one decade on, their numbers show no sign of recovering.
The trends are worrying especially because we still have no idea what’s behind them. It’s telling that all of the five stable populations lived in protected areas, while the crashing species hailed from regions troubled by human activity. Their fates could be driven by falling habitat quality and a lack of prey. It’s also notable that all but one of the stable five are wide-ranging and active foragers, while the declining species are typically ambush predators that stay in the same restricted range. These “sit-and-wait” hunters are more vulnerable to human activity that disrupts the habitats they need to hide in, and they usually grow and breed slowly.
Whatever the cause, it seems to be universal. Reading’s team found that tropical species like Nigeria’s rhinoceros viper are experiencing similar population crashes as temperate ones like the British smooth snake, and all within the same period of time. To Reading, this suggests that the declines share a common and widespread cause – climate change would be an obvious candidate but that needs to be tested.
Reference: Biology Letters http://dx.doi.org/10.1098/rsbl.2010.0373
More from the Guardian
Deep beneath the ocean’s surface lie the “black smokers“, undersea chimneys channelling superheated water from below the Earth’s crust. Completely devoid of sunlight, they are some of the most extreme environments on the planet. Any creature that can survive their highly acidic water, scorching temperatures and crushing pressures still has to contend with assaults from predatory crabs. What better place, then, to look for the next generation of body armour technology?
The scaly-foot gastropod (Crysomalion squamiferum) was discovered just 9 years ago at an Indian black smoker and it may have one of the most effective animal armours so far discovered. Its shell is a composite, made of three layers, each with different properties and made of different minerals. Together, they form a structure that’s completely unlike any known armour, whether natural or man-made. It can protect the animal from the searing heat of its habitat, stop its precious minerals from dissolving away in the acidic water and resist the crushing, penetrating, peeling claw-attacks of predatory crabs.
Animals have been protecting themselves with armour long before humans starting shaping steel and Kevlar. To create a protective covering, human designers must account for a mind-boggling array of physical traits including thickness, geometry, strength, elasticity and more. But evolution can take all of those factors into account without the guiding hand of a designer, putting thousands of structures through the test of natural selection and weeding out the best combinations. The results are the culmination of millions of years of research and development and they are striking in their effectiveness.
Haimin Yao from MIT works in the lab of Catherine Ortiz, a group that has been studying the defences of animals including sea urchins, chitons, a group of marine molluscs, to the Senegal bichir, a type of armoured fish.
Yao discovered the secrets behind the snail’s shell by slicing through it in cross-sections and studying its structure at a nanometre level. He even attacked it with a diamond-tipped probe, to simulate the crushing attacks of the crabs that frequent the black smokers. Using this data, Yao created a virtual simulation of the shell and put it through a digital crash-test, crab claws and all.
Our teeth are a mystery. The set we grow during late childhood stays with us throughout our lives, biting and chewing thousands of times a day. They can withstand forces of up to 1,000 newtons and yet, the material that coats them – enamel – is little tougher than glass. How does this extraordinarily brittle substance not shatter into pieces every time we crunch a nut or chomp on an apple?
Herzl Chai from Tel Aviv University found the answer, and it’s a surprising one. At a microscopic level, our teeth defend against fractures by developing with cracks already built in. These pre-made defects are known as “tufts” because of their wavy appearance. They are scattered throughout the enamel and share any physical burdens placed on a tooth, so that no one part has to take the full brunt.
By pressing down on individual teeth using a metal rod, Chai found that it’s relatively easy to create a crack in a tooth, but much harder to actually make it grow bigger to the point where the tooth properly breaks. The tufts, together with structures that prevent cracks from growing, are responsible – they allow us to chew without catastrophe. Our teeth aren’t built to avoid damage, but they’re incredibly good at containing it.
Humans aren’t alone in this – Chai compared out teeth to those of sea otters, and found the same adaptive features under a microscope. It may seem like an odd pairing, but we share a fondness for hard-shelled foods with sea otters – we like nuts and seeds, while they can’t get enough of shellfish. These similarities are reflected in our teeth.
In the late 19th century, asbestos became a building material of choice. Resistant to heat, electricity and corrosion, it found many uses including home insulation, brake pads and ship-building. By the time that the first health problems were reported, the material was commonplace. In the UK, the material was only restricted in 1983 after thousands of people were exposed during the post-war era. The result is a latent epidemic of related diseases including a rare type of cancer called mesothelioma, which is becoming more common and is only expected to peak in incidence over the next decade or so.
The glacial pace with which governments started to regulate asbestos use has put thousands of lives in jeopardy and it’s a disaster that we could do with not repeating. But while asbestos is yesterday’s construction material, a new substance being heralded as the building material of tomorrow has the potential to cause similar health risks – carbon nanotubes.
A new study suggests that carbon nanotubes can cause asbestos-like damage if they are injected into the bodies of mice. The results are cause for concern but not panic. The study didn’t show that the nanotubes can build up in body cavities of their own accord, nor if this damage would eventually result in the mesotheliomas that asbestos can cause. It does however show that we are running before we can walk if the widespread commercial use of carbon nanotubes goes unregulated without rigorous research on their safety.
Imagine that you hand is made of jelly and you have to carve a roast using a knife that has no handle. The bare metal blade would rip through your hypothetical hand as easily as it would through the meat. It’s clearly no easy task and yet, squid have to cope with a very similar challenge every time they eat a meal.
The bodies of squid, like those of their relatives the cuttlefish and octopus, are mainly soft and pliant, with one major exception. In the centre of their web of tentacles lies a hard, sharp and murderous beak that resembles that of a parrot. The beak is a tool for killing and dismembering prey and the large Humboldt squid (Dosidicus gigas) is known to use its beak to sever the spinal cord of fishy prey, paralysing them for easy dining.
The Humboldt squid’s beak is two inches long and incredibly hard (difficult to dent or scratch), stiff (difficult to bend out of shape) and tough (resistant to fractures). This combination of properties makes the beak harder to deform than virtually all known metals and polymers. That’s all the more remarkable because unlike most animal teeth or jaws, it contains no minerals or metals. It’s made up solely of organic chemicals and manages to be twice as hard and stiff as the most competitive manmade equivalents.
By comparison, the mass of muscle that surrounds and connects to the beak is incredibly soft, the equivalent of a jelly hand gripping a bare metal blade. With such mismatched tissues, how does the squid manage to use its killer mouth without tearing the surrounding muscle to shreds?