Bees.

Bees mean a lot to us: producers of honey; pollinators of crops and an exemplar for roboticists hoping to emulate their swarm intelligence. Archaeologists have found evidence of beekeeping in the Middle East dating back at least 3000 years, lending credence to the Bible’s description of Israel as “a land flowing with milk and honey”.

Perhaps the most fascinating thing about honeybees in particular is their cooperative way of life, which biologists call eusociality. Most individuals in a colony do not reproduce, instead working as devoted servants to one breeding female.

The queen can hardly relax and enjoy the trappings of power, however. Instead she spends her whole life making eggs, up to 1500 in a day – more than her body weight. Fertilised eggs develop into females, who generally become non-breeding workers. The queen can also lay unfertilised eggs, which develop into male bees, called drones. Their job is to find a queen from another colony and mate with her. After the act, his genitals are ripped from his body and he dies.

Queens live for up to seven years, but they become less productive as they get older. When the queen stops producing eggs, the workers select a new queen. Instead of pollen and honey, they feed her royal jelly, which workers secrete from glands in their heads. She develops inside a special queen cell, becomes sexually mature, then chews her way out. In some colonies, there may be multiple new queens, who fight each other to the death. The survivor will fly to a drone congregation area and mate with around a dozen drones, storing up to 6 million sperm in her body.

The selfless behaviour of the non-breeding workers may be explained by honeybees’ unusual sex determination system, called haplodiploidy. Being derived from unfertilised eggs, males have only one set of chromosomes instead of the usual two, and therefore all their sperms are identical. That means that female workers are more closely related to their sisters than to their own potential offspring, so in theory more of their genes are passed on if they help to raise their sisters. This idea, developed by William Hamilton, was one of the inspirations for the “selfish gene” view of evolution popularised by Richard Dawkins.

However, it doesn’t hold true if the queen mates with multiple males. Nevertheless, some biologists argue that it still can explain the evolution of eusociality, because eusocial species of insects were monogamous to begin with.

Bee afraid

It’s easy to forget that honeybees are just one, quite unusual type of bee. There are 20,000 species, and most are solitary: all females are fertile and have their own nests without workers.

Many of these species are in decline, with insecticide use, habitat destruction and climate change among the drivers. But it is not all bad news. According to a recent UK report, a key group of 22 wild bees and hoverflies that we rely on to pollinate our crops has been doing relatively well. The concern is that we are losing some of the rarer species, such as the red-shanked carder bee.

In 2006, beekeepers around the world began reporting a new problem, named colony collapse disorder, in which most of the worker bees in a colony disappeared. Exactly why this happens is still uncertain, but biologists think that intensive agriculture and industry have created a range of stressors that do not kill bees, but impair their ability to forage and find their way home. Pests and parasites such as the varroa mite may also be to blame for some cases.

A group of pesticides called neonicotinoids are another major concern. The European Union decided to ban the outdoor use of these compounds in 2018, after field trials showed harmful effects on bee reproduction. However, ecologists warn that other pesticides may be just as bad.

Hive mind

Beyond their crucial role as pollinators, bees are of particular interest to cognition researchers looking to understand how they manage quite complicated tasks with such limited brainpower. One aspect of their behaviour that has long fascinated biologists is the waggle dance: a sequence of movements that communicates directions to food sources, first decoded by Karl von Frisch in 1946. Tim Landgraf at the Free University of Berlin in Germany built a waggle-dancing robot in an effort to speak to bees in their own language.

Their communication skills don’t end there. Honeybees use a rich repertoire of vibrational signals to send messages, including a “get to work” signal, a request for grooming and even an expression of surprise.

Researchers have shown that bees can learn to pull a string or move a ball to get a food reward – the only recorded case of invertebrates using tools. Other experiments suggest they have a basic grasp of numbers and even experience something akin to emotions. Sam Wong