Panama’s San Lorenzo forest reserve is around the size of Manhattan. For two years, this small area was host to 102 scientists, working together to count everything that crept and crawled. They came from 17 countries, and converged upon a half-hectare of the forest, about the size of half a rugby pitch. They dug into the soil, and ascended into the 40-metre-tall treetops with ropes, balloons, and a giant crane. They unleashed fogs, set up sticky traps, and hacked into pieces of wood.
Together, they were part of the largest ever systematic attempt to answer a disarmingly simple question: in a patch of tropical rainforest, how many species of insects and other arthropods are there?
After collecting the critters in 2003 and 2004, and analysing the material for eight years, they got an answer: 6,144 species in that patch of forest. Using computer simulations to scale that up, they estimate that the entire 6,000-hectare Manhattan-sized forest is home to around 25,000 arthropod species.
If you travelled back to Spain, during the Cretaceous period, you might see an insect so bizarre that you’d think you were hallucinating. That’s certainly what Ricardo Pérez-de la Fuente thought when he found the creature entombed in amber in 2008.
The fossilised insect of the larva of a lacewing. Around 1,200 species of lacewings still exist, and their larvae are voracious predators of aphids and other small bugs. They also attach bits of garbage to tangled bristles jutting from their backs, including plant fibres, bits of bark and leaf, algae and moss, snail shells, and even the corpses of their victims. Dressed as walking trash, the larvae camouflage themselves from predators like wasps or cannibalistic lacewings. And even if they are found, the coats of detritus act as physical shields.
We now know that this strategy is an ancient one, because the lacewing in De la Fuente’s amber nugget—which is 110 million years old—also used it. It’s barely a centimetre long, and has the same long legs, sickle-shaped jaws, and trash-carrying structures of modern lacewing larvae. But it took camouflage to even more elaborate extremes. Rather than simple bristles, it had a few dozen extremely long tubes, longer even than the larva’s own body. Each one has smaller trumpet-shaped fibres branching off from it, forming a large basket for carrying trash.
De la Fuente called it Hallucinochrysa diogenesi, a name that is both evocative and cheekily descriptive. The first part comes from the Latin “hallucinatus” and references “the bizarreness of the insect”. The second comes from Diogenes the Greek philosopher, whose name is associated with a disorder where people compulsively hoard trash.
When Malcolm Burrows first heard the sound of a pygmy mole cricket leaping from water, he was enjoying a sandwich. Burrows, a zoologist from the University of Cambridge, was visiting Cape Town and had snuck out the back of the local zoology department to eat his lunch by a pond. “I heard sporadic thwacking noises coming from the water,” he says. “When I looked more closely I could see small black insects jumping repeatedly from the water and heading towards the bank.”
They were pygmy mole crickets, a group of tiny insects just a few millimetres long. Despite their name, they’re more grasshoppers than crickets, and are some of the most primitive members of this group. They’re found on every continent except Antarctica.
Pygmy mole crickets cannot fly, but they can certainly jump. Burrows collected some of the individuals from the pond, and took them back to the lab to film them with high-speed cameras. When they take off, they often spin head-over-tail, but what they lack in elegance they make up for in distance. They can jump over 1.4 metres, more than 280 times their own body length.
Doing this on land is one thing, but as Burrows saw at the pond, these insects can also jump from water. This ability serves them well—they live in burrows near to fresh water, which frequently flood. Their leaps send them back to terra firma, saving their lives.
Burrows found that these insects jump from water in a completely new way. Animals like pond-skaters and the basilisk lizard can walk on water by relying on surface tension—the tendency of the surface of water to resist an external force. But the mole cricket extends its hind legs so quickly that they break right through the surface.
As the legs move through the water, three pairs of flat paddles and two pairs of long spurs flare out from each one. These structures have a concave shape, much like an oar. As they flare out, they increase the surface area of the mole cricket’s leg by around 2.4 times, allowing it to push down on a much larger volume of water. And once the legs are fully extended, the paddles retract to reduce the drag on the airborne insect. From water, the mole crickets can only jump for 3 centimetres or so. That’s pathetic compared to their land-based attempts, but still more than 5 times their body length, and enough to save them from drowning.
When Burrows shone ultraviolet light onto the paddles, they glowed with a bright blue colour at their bases. That’s the signature of resilin, an incredibly elastic protein that powers the jumps and wingbeats of many insects. Its presence on the mole cricket suggests that the paddles and spurs are spring-loaded.
“It just shows what amazing things can be found close to where we live and work,” says Burrows. “Instead of spending time exploring the more exotic parts of South Africa, I spent most of my visit there essentially looking outside my back door.”
Reference: Burrows & Sutton. 2012. Pygmy mole crickets jump from water. Current Biology 22: R990
All photos and video by Malcolm Burrows
A very hungry caterpillar munches on a cabbage leaf and sets off an alarm. The plant releases chemicals into the air, signalling that it is under attack. This alarm is intercepted by a wasp, which stings the caterpillar and implants it with eggs. When they hatch, the larval wasps devour their host from the inside, eventually bursting out to spin cocoons and transform into adults. The cabbage (and those around it) are saved, and the wasp—known as a parasitoid because of its fatal body-snatching habits—raises the next generation.
But that’s not the whole story.
Some parasitic wasps are “hyperparasitoids”—they target other parasitoid wasps. And they also track the cabbage’s alarm chemicals, so they can find infected caterpillars. When they do, they lay their eggs on any wasp grubs or pupae that they find. Their young devour the young of the other would-be parasites, in a tiered stack of body-snatching. It’s like a cross between the films Alien and Inception.
Absence can speak volumes. The lack of sediment in a flat piece of ground—a track—can testify to the footstep of a dinosaur that once walked on it. The lack of minerals in a solid shell—a hole—can reveal the presence of parasite that was once trapped in it. The world’s museums are full of such “trace fossils”, but so are many of the world’s art galleries.
The image above is taken from a woodcut currently residing in Amsterdam’s Rijksmuseum. It was made by etching a pattern into a block of wood, so that the remaining raised edges could be dipped in ink and used to print an image. These woodcuts were the main way of illustrating European books between the 15th and 19th centuries, and were used for at least 7 million different titles.
But as you can see, the print is littered with tiny white holes. These are called wormholes, and inaccurately so—they’re actually the work of beetles. The adults laid their eggs in crevices within the trunks of trees. The grubs slowly bored their way through the wood, eventually transformed into adults, and burrowed their way out of their shelters. The artists who transformed the tree trunks into printing blocks also inherited the exit-holes of the adult beetles, which left small circles of empty whiteness when pressed onto pages.
The beetles only emerged a year or so after the blocks were carved. The holes they left must have been frustrating, but remaking them would have been expensive. So the blocks were kept and reused despite their defects, unless the beetles had really gone to town. The holes they left behind preserve a record of wood-boring beetles, across four centuries of European literature. These holes are trace fossils. They’re evidence of beetle behaviour that’s been printed into old pages, just as dinosaur tracks were printed into the earth.
Now, Blair Hedges from Pennsylvania State University has used these fossils to study the history of the beetles that made them.
Every time you put on some music or listen to a speaker’s words, you are party to a miracle of biology – the ability to hear. Sounds are just waves of pressure, cascading through sparse molecules of air. Your ears can not only detect these oscillations, but decode them to reveal a Bach sonata, a laughing friend, or a honking car.
This happens in three steps. First: capture. The sound waves pass through the bits of your ear you can actually see, and vibrate a membrane, stretched taut across your ear canal. This is the tympanum, or more evocatively, the eardrum. On the other side, the eardrum connects to three tiny well-named bones—the hammer, anvil and stirrup—which link the air-filled outer ear with the fluid-filled inner ear.
The bones perform the second-step: convert and amplify. They transmit all the pressure from the relatively wide eardrum into the much tinier tip of the stirrup, transforming large but faint air-borne vibrations into small but strong fluid-borne ones.
These vibrations enter the inner ear, which looks like a French whisk poking out of a snail shell. Ignore the whisk for now – the shell is the cochlea, a rolled-up tube that’s filled with fluid and lined with sensitive hair cells. These perform the third step: frequency analysis. Each cell responds to different frequencies, and are neatly aligned so that the low-frequency ones are at one end of the tube and the high-frequency ones at another. They’re like a reverse piano keyboard that senses rather than plays. The signals from these cells are passed to the auditory nerve and decoded in the brain. And voila – we hear something.
All mammal ears work in the same way: capture sound; convert and amplify; and analyse frequencies. But good adaptation are rarely wasted on just one part of the tree of life. Different branches often evolve similar solutions to life’s problems. And that’s why, in the rainforests of South America, a katydid—a relative of crickets—hears using the same three-step method that we use, but with ears that are found on its knees.
The thing in the photo above, I’m sad to say, is a penis. It belongs to the male seed beetle. And just in case you’re holding out hope that appearances are deceiving, I can assure you they are not. Those spikes are hard and sharp, and they inflict heavy injuries upon the female beetles during sex. Why would such a hellish organ evolve?
This isn’t just about beetles. The animal kingdom is full of bafflingly-shaped penises adorned with spines, spikes, and convoluted twists and turns. In some animal groups, like certain flies, penis shape is the only clue that allows scientists to distinguish between closely related species.
For a male, sex isn’t just about penetration. After he ejaculates inside a female, his sperm still have to make their way to her eggs to fertilise them and pass on his genes. If she mates with many suitors, her body becomes a battleground where the sperm of different males duke it out. Females can influence this competition by being choosy over mates, storing sperm in special pouches, or evolving their own convoluted genital passages. Males, meanwhile, have evolved their own tricks, including: guarding behaviour; self-castration; barbed sperm; chemical weapons in their sperm; mating plugs; ‘traumatic insemination’; and having lots of sperm.
And spiky penises. That too.
The dung beetle, Scarabaeus nigroaeneus, as its name suggests, eats the faeces of large grazing mammals. When it finds a fresh pat, it fashions the dung into a ball and rolls it home, head down and walking backwards. That’s hard work. The balls can be 50 times heavier than the beetle, whose body heats up as it pushes around its weighty cargo.
Heating up is something that an insect can’t afford to do in the South African desert, where the ground can reach a scorching 60 degrees Celsius in the middle of the day. But the beetle’s dung-rolling antics provide it with a constantly accessible way of beating the heat. By filming dung beetles with a heat-sensitive camera, Jochen Smolka from Lund University has found that their dung balls aren’t just take-away meals—they’re also portable coolers.
In North America’s Sonoran desert, there’s a fly that depends on a cactus. Thanks to a handful of changes in a gene called Neverland, Drosophila pachea can no longer make chemicals that it needs to grow and reproduce. These genetic changes represent the evolution of subservience – they inextricably bound the fly to the senita cactus, the only species with the substances the fly needs.
The Neverland gene makes a protein of the same name, which converts cholesterol into 7-dehydrocholesterol. This chemical reaction is the first of many that leads to ecdysone – a hormone that all insects need to transform from a larva into an adult. Most species make their own ecdysone but D.pachea is ill-equipped. Because of its Neverland mutations, the manufacturing process fails at the very first step. Without intervention, the fly would be permanently stuck in larval mode. Hence the name, Neverland—fly genes are named after what happens to the insect when the gene is broken.
Fortunately, in the wild, D.pachea can compensate for its genetic problem by feeding on the senita cactus. The cactus produces lathosterol—a chemical related to cholesterol. D.pachea’s version of Neverland can still process this substitute, and uses it to kickstart the production of ecdysone.
The senita is the only plant in the Sonoran desert that makes lathosterol, the only one that lets the fly bypass the deficiency that would keep it forever young. It has become the fly’s dealer, pushing out chemicals that it cannot live without, and all because of changes to a single fly gene.
A different version of this story appears at The Scientist.
Honeybee workers spend their whole lives toiling for their hives, never ascending to the royal status of queens. But they can change careers. At first, they’re nurses, which stay in the hive and tend to their larval sisters. Later on, they transform into foragers, which venture into the outside world in search of flowers and food.
This isn’t just a case of flipping between tasks. Nurses and foragers are very distinct sub-castes that differ in their bodies, mental abilities, and behaviour – foragers, for example, are the ones that use the famous waggle dance. “[They’re] as different as being a scientist or journalist,” explains Gro Amdam, who studies bee behaviour. “It’s really amazing that they can sculpt themselves into those two roles that require very specialist skills.” The transformation between nurse and forager is significant, but it’s also reversible. If nurses go missing, foragers can revert back to their former selves to fill the employment gap.
Amdam likens them to the classic optical illusion (shown on the right) which depicts both a young debutante and an old crone. “The bee genome is like this drawing,” she says. “It has both ladies in it. How is the genome able to make one of them stand out and then the other?
The answer lies in ‘epigenetic’ changes that alter how some of the bees’ genes are used, without changing the underlying DNA. Amdam and her colleague Andrew Feinberg found that the shift from nurse to forager involves a set of chemical marks, added to the DNA of few dozen genes. These marks, known as methyl groups, are like Post-It notes that dictate how a piece of text should be read, without altering the actual words. And if the foragers change back into nurses, the methylation marks also revert.
Together, they form a toolkit for flexibility, a way of seeing both the crone and the debutante in the same picture, a way of eking out two very different and reversible skill-sets from the same genome.