A.ervi attacks a pea aphid, by Alexander Wild
In a British lab, a wasp has become (locally) extinct. And then, another wasp follows it into oblivion. That’s odd because these two insects are not competitors. They don’t attack one another, and they don’t even eat the same food. They do, however, remind us that it’s very hard to predict how the decline of one species will affect those around it.
Some consequences are obvious. If an animal goes extinct, its loss will cascade up and down the food web, so that its predators will suffer but its prey will probably thrive. But food webs are webs for a reason, rather than a set of isolated linear “food chains”. Consequences can ripple across, as well as up and down.
Sticking to surfaces and walking up walls are so commonplace among insects that they risk becoming boring. But the green dock beetle has a fresh twist on this tired trick: it can stick to surfaces underwater. The secret to its aquatic stride is a set of small bubbles trapped beneath its feet. This insect can plod along underwater by literally walking on air.
The green dock beetle (Gastrophysa viridula) is a gorgeous European resident with a metallic green shell, occasionally streaked with rainbow hues. It can walk on flat surfaces thanks to thousands of hairs on the claws of their feet, which fit into the microscopic nooks and crannies of whatever’s underfoot. Most beetles have the same ability, and some boost the adhesive power of their hairs by secreting a sticky oil onto them.
These adaptations work well enough in dry conditions, but they ought to fail on wet surfaces. Water molecules should interfere with the hairs’ close contact, and disrupt the adhesive power of the oil. “People believed that beetles have no ability to walk under water,” says Naoe Hosoda from the National Institute for Material Science in Tuskuba, Japan.
They were clearly wrong. Together with Stanislav Gorb from the Zoological Institute at the University of Kiel, Germany, she clearly showed that the green dock beetle has no problems walking underwater. The duo captured 29 wild beetles, and allowed them to walk off a stick onto the bottom of a water bath. Once there, they kept on walking. Read More
If wasps didn’t exist, picnics would be a lot more fun. But the next time you find yourself trying to dodge a flying, jam-seeking harpoon, think about this: without wasps, many of your ingredients might not exist at all. Irene Stefanini and Leonardo Dapporto from the University of Florence have found that the guts of wasps provide a safe winter refuge for yeast – specifically Saccharomyces cerevisiae, the fungus we use to make wine, beer and bread. And without those, picnics would be a lot less fun.
S.cerevisiase has been our companion for at least 9,000 years, not just as a tool of baking and brewing, but as a doyen of modern genetics. It has helped us to make tremendous scientific progress and drink ourselves into stupors, possibly at the same time. But despite its significance, we know very little about where the yeast came from, or how it lives in the wild.
The wild strains do grow on grapes and berries, but only found on ripe fruits rather than pristine ones. And they’re usually only found in warm summery conditions. So, where do they go in the intervening months, and how do they move around? They certainly can’t go airborne, so something must be carrying them.
Stefanini and Dapporto thought that wasps were good candidates. They’re active through the summer, when they often eat grapes. Fertilised females hibernate through the winter and start fresh colonies in the spring, feeding their new larvae with regurgitated food. In the digestive tracts of wasps, yeasts could get a ride from grape to grape, from one wasp generation to the next, and from autumn to spring.
There are thousands of termite species, and many engage in chemical warfare. Some squirt noxious chemicals from nozzles on their heads. Others violently rupture their own bodies to release sticky immobilising fluids, sacrificing themselves for the good of their sisters. Their range of weapons is astounding, and Jan Sobotnik from the Academy of Sciences of the Czech Republic and Thomas Bourguignon from the Université Libre de Bruxelles have just found a new one.
They were studying the termite Neocapritermes taracua when he noticed that some workers have a pair of dark blue spots in the gap between their torsos and abdomens. When other termites attack their colony, the blue workers bite the intruders and burst, releasing a drop of fluid that soon becomes sticky gel. Watch it happen in the video below – the black dot in the middle of the droplet are intestines and other internal organs).
Some folks just can’t help being loud in bed, but noisy liaisons can lead to a swift death… at least for a housefly. In a German cowshed, Natterer’s bats eavesdrop on mating flies, homing in on their distinctive sexual buzzes.
Based on some old papers, Stefan Greif form the Max Planck Institute for Ornithology knew that Natterer’s bats shelter in cowsheds and sometimes feed on the flies within. What he didn’t know was how the bats catch insects that they shouldn’t be able to find. They hunt with sonar, releasing high-pitched squeaks and visualising the world in the returning echoes. Normally, the echoes rebounding from the flies would be masked by those bouncing off the rough, textured surface of the shed’s ceiling. The flies should be invisible.
And they mostly are. Greif filmed thousands of flies walking on the shed’s ceiling, and not a single one of them was ever targeted by a bat. That changed as soon as they started having sex. Greif found that a quarter of mating flies are attacked by bats. Just over half of the attacks were successful and in almost all of these, the bat swallowed both partners.
A malarial mosquito is a flying factory for Plasmodium – a parasite that fills its guts, and storms the blood of every person it bites. By hosting and spreading these parasites, mosquitoes kill 1.2 million people every year.
But Plasmodium isn’t the only thing living inside a mosquito’s guts. Just as our bowels are home to trillions of bacteria, mosquitoes also carry their own microscopic menageries. Now, Sibao Wang from Johns Hopkins Bloomberg School of Public Health has transformed one of these bacterial associates into the latest recruit in our war against malaria. By loading it with genes that destroy malarial parasites, Wang has turned the friend of our enemy into our friend.
Many groups of scientists have tried to beat malaria by genetically modifying the species of mosquito that carries it – Anopheles gambiae. Marcelo Jacobs-Lorena, who led Wang’s new study, has been at the forefront of these efforts. In 2002, his team loaded mosquitoes with a modified gene so that their guts produce a substance that kills off Plasmodium.
Illustration by Inna-Marie Strazhnik
Some flies, known as phorids, specialise in decapitating ants in a gruesome way. They lay their eggs inside their victims. When the maggots hatch, they move towards the ant’s head, where they gorge upon the brain and other tissues. The ant stumbles about in a literally mindless stupor until the connection between its head and body is dissolved by a enzyme released from the maggot. The head falls off and the adult flies burst out.
There are hundreds of species of phorid flies, each one targeting its own preferred ants. But some ants are naturally defended against these parasites because they’re incredibly small. Most phorids are a few millimetres long. If an ant is the same size, its head wouldn’t be roomy enough for a developing fly. Thailand, for example, is home to an acrobat ant (Crematogaster rogenhoferi) which can be just 2 millimetres long. Surely these workers are safe from decapitating parasites?
No, they’re not. Brian Brown from the Natural History Museum of Los Angeles County has just discovered a Thai phorid that’s just 0.4 millimetres in length. It’s the world’s tiniest fly, small enough to sit comfortably on the eye of a common housefly. It’s easily small enough to fit inside the head of even the smallest acrobat ant. It just goes to show that there is no way of truly escaping from parasites. If you evolve a miniscule body, they will shrink even further in pursuit.
One minute, a cockroach is running headfirst off a ledge. The next minute, it’s gone, apparently having plummeted to its doom. But wait! It’s actually clinging to the underside of the ledge! This cockroach has watched one too many action movies.
The roach executes its death-defying manoeuvre by turning its hind legs into grappling hooks and its body into a pendulum. Just as it is about to fall, it grabs the edge of the ledge with the claws of its hind legs, swings onto the underneath the ledge and hangs upside-down. In the wild, this disappearing act allows it to avoid falls and escape from predators. And in Robert Full’s lab at University of California, Berkeley, the roach’s trick is inspiring the design of agile robots.
Full studies how animals move, but his team discovered the cockroach’s behaviour by accident. “We were testing the animal’s athleticism in crossing gaps using their antennae, and were surprised to find the insect gone,” says Full. “After searching, we discovered it upside-down under the ledge. To our knowledge, this is a new behavior, and certainly the first time it has been quantified.”
The largest wings of any living insect belong to the Queen Alexandra birdwing butterfly and the atlas moth. They can span 10 to 12 inches across. But even these giants are puny compared to the insects of prehistory. Meganeura, for example, was a dragonfly that lived 300 million years ago and each of its wings was the length of my arm. Why do such behemoths no longer exist?
The prevailing theory, proposed around a century ago, is that the Earth’s atmosphere used to have much more oxygen—more than 30 per cent in the Permian, compared to just 20 today. This vital gas sets an upper limit on how big animals can be. The seething quantities of past eras allowed flying insects to fuel faster metabolisms and larger bodies.
Matthew Clapham and Jered Karr from the University of California, Santa Cruz have now found some strong evidence to support this idea, after analysing more than 10,500 fossilised insect wings. It took almost 18 months to collect the entire data set, but it clearly showed that the maximum wingspans of flying insects neatly tracked the oxygen in the atmosphere for their first 150 million years of evolution. As the gas reached its peak during the Permian, the insects were at their largest. As levels later fell, the insects shrank.
But this neat correlation stopped between 130 and 140 million years ago, during the early Cretaceous period. Even though oxygen concentrations started climbing from a Jurassic low of 15 per cent, for the first time in their history, the insects didn’t follow suit. If anything, they got smaller. They had finally encountered something that limited their growth more than the oxygen in the air: birds.
In the 1940s, visitors watching football games at Berkeley’s Californian Memorial Stadium would often be plagued by beetles. The insects swarmed their clothes and bit them on the necks and hands. The cause: cigarettes. The crowds smoked so heavily that a cloud of smoke hung over the stadium. And where there’s smoke, there’s fire. And where there’s fire, there are fire-chaser beetles.
While most animals flee from fires, fire-chaser beetles (Melanophila) head towards a blaze. They can only lay their eggs in freshly burnt trees, whose defences have been scorched away. Fire is such an essential part of the beetles’ life cycle that they’ll travel over 60 kilometres to find it. They’re not fussy about the source, either. Forest fires will obviously do, but so will industrial plants, kilns, burning oil barrels, vats of hot sugar syrup, and even cigarette-puffing sports fans.
The beetles find fire with a pair of pits below their middle pair of legs. Each is only as wide as a few human hairs, and consists of 70 dome-shaped sensors. They look a bit like insect eyes. In the 1960s, scientists showed that the sensors detect the infrared radiation given off by hot objects. Each one is filled with liquid, which expands when it absorbs infrared radiation. This motion stimulates sensory cells and tells the beetle that there’s heat afoot.