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.
Throughout North America, honeybees are abandoning their hives. The workers are often found dead, some distance away. Meanwhile, the hives are like honeycombed Marie Celestes, with honey and pollen left uneaten, and larvae still trapped in their chambers.
There are many possible causes of this “colony collapse disorder” (CCD). These include various viruses, a single-celled parasite called Nosema apis, a dramatically named mite called Varroa destructor, exposure to pesticides, or a combination of all of the above. Any or all of these factors could explain why the bees die, but why do the workers abandon the hive?
Andrew Core from San Francisco State University has a possible answer, and a new suspect for CCD. He has shown that a parasitic fly, usually known for attacking bumblebees, also targets honeybees. The fly, Apocephalus borealis, lays up to a dozen eggs in bee workers. Its grubs eventually eat the bees from the inside-out. And the infected workers, for whatever reason, abandon their hives to die.
When we make decisions, our brains are abuzz with agreements and vetoes. Groups of neurons represent different choices, and interact with one another until one rises to the fore. The neurons excite some of their neighbours into firing in tandem, while suppressing others into silence. From this noisy cross-talk, a choice emerges.
The same thing happens in a bee hive. The entire colony, consisting of tens thousands of individuals, works like a single human nervous system, with each bee behaving like a neuron. When they make a decision, such as choosing where to build a nest, individual bees opt for different choices and they support and veto each other until they reach a consensus. They have, quite literally, a hive mind.
Bumblebees begin their adult lives by eating their sisters’ faeces. After many months as helpless, hungry larvae, they spin a silken cocoon and transform their bodies. When they emerge, ready to face the world, they get mouthfuls of poo. It may not sound like an auspicious start, but it’s essential. The faeces contain special bacteria that act as part of the bee’s immune system, protecting it from an incredibly dangerous parasite.
Gut bacteria are important partners for many animals. We humans have up to 100 trillion microbes in our bowels, and this “microbiota” outnumbers our own cells by ten to one. They act like a hidden, writhing organ. They break down our food. They influence our behaviour. And they safeguard our health by crowding out other bacteria that could cause disease. It seems that gut bacteria play a similar role in bumblebees.
In Australia, the penalty for burglary is several years in prison. But that’s for humans. For the small hive beetle, breaking and entering into the hive of stingless bees carries a far harsher sentence – being mummified alive in a sticky tomb of wax, mud and resin.
Bees can communicate with each other using the famous “waggle dance”. With special figure-of-eight gyrations, they can accurately tell other hive-mates about the location of nectar sources. Karl von Frisch translated the waggle dance decades ago but it’s just a small part of bee communication. As well as signals that tell their sisters where to find food, bees have a stop signal that silences dancers who are advertising dangerous locations.
The signal is a brief vibration at a frequency of 380 Hz (roughly middle G), that lasts just 150 milliseconds. It’s not delivered very gracefully. Occasionally, the signalling bee will use a honeycomb to carry her good vibrations, but more often than not, she’ll climb on top of another bee first or use a friendly headbutt. The signal is made when bees have just travelled back from a food source where they were attacked by rivals or ambush predators. And they always aim their buzzes at waggle dancers. The meaning is clear; it says, “Don’t go there.”
These signals were identified decades ago, but scientists originally interpreted them as a begging call, intended to cadge some food of another worker. It seems like a strange conclusion, when you consider that the signals never actually prompt workers to exchange food. Their true nature became clearer when scientists showed that playing them through speakers could stop dancers from waggling.
The mighty insect colonies of ants, termites and bees have been described as superorganisms. Through the concerted action of many bodies working towards a common goal, they can achieve great feats of architecture, agriculture and warfare that individual insects cannot.
That’s more than just an evocative metaphor. Chen Hou from Arizona State University has found that the same mathematical principles govern the lives of insect colonies and individual animals. You could predict how quickly an individual insect grows or burn food, how much effort it puts into reproduction and how long it lives by plugging its body weight into a simple formula. That same formula works for insect colonies too, if you treat their members as a collective whole.
Life is fundamentally about the use of energy, about effectively harvesting it from food and channelling it into existence and offspring. As animals get bigger, their changing use of energy ripples across all aspects of their lives. Because of economies of scale, larger and more complex animals need less energy for each individual cell. They grow and reproduce more slowly and they live longer.
The astounding thing is that this variety can be captured by a deceptively simple equation. An animal’s metabolic rate is proportional to its mass to the power of three-quarters (0.75). So a cat that is 100 times heavier than a mouse would have a metabolic rate that was around 32 times greater, and a human that is 10 times heavier than a cat would have a metabolic rate around 6 times greater. This beautiful three-quarters “power law” links all animals from mice to elephants.
Hou showed that it applies to insect colonies. He gathered data on over 168 species of social insects and noted the total mass of all their members. They ranged from species of fire ants whose colonies weigh little more than 2 milligrams, to African termite colonies that tip the scales at around 4kg.
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
It’s a myth that elephants are afraid of mice, but new research shows that they’re not too keen on bees. Even though they fearlessly stand up to lions, the mere buzzing of bees is enough to send a herd of elephants running off. Armed with this knowledge, African farmers may soon be able to use strategically placed hives or recordings to minimise conflicts with elephants.
Iain Douglas-Hamilton and Fritz Vollrath from Kenyan conservation charity Save the Elephants first suspected this elephantine phobia in 2002, when they noticed that elephants were less likely to damage acacia trees that contained beehives.
Animals as powerful as the African elephant can go largely untroubled by predators. Their bulk alone protects them from all but the most ambitious of lion prides.
But these defences do nothing against the African bees, which can sting them in their eyes, behind their ears and inside their trunks. Against these aggressive insects, the elephants are well justified in their caution and local people have reported swarms of bees chasing elephants for long distances.
Lucy King, a graduate student from the University of Oxford confirmed this theory by using camouflaged wireless speakers to play recordings of angry buzzing bees to herds of elephants resting under trees.