How Honey Bees Keep Ecosystems Running: Pollination Facts

The western honey bee (Apis mellifera) is one of around 20,000 bee species, but it is the one that moves at agricultural scale. A single managed colony holds 20,000 to 60,000 workers at its summer peak, forages over an area of several square kilometres, and can be loaded onto a truck. Every February more than two million colonies are driven into California to pollinate almonds, the largest managed pollination event in the world.

The numbers behind that are worth having straight. A 2007 review in Proceedings of the Royal Society B by Alexandra-Maria Klein and colleagues found that 87 of the 115 leading global food crops depend to some degree on animal pollination, and that those crops make up about 35 percent of global crop production by volume. Staples such as wheat, rice, and maize are wind-pollinated; the fruit, nuts, vegetables, and oilseeds that provide most of our vitamins are not. In the United States the USDA puts the value of honey bee pollination at around 15 billion dollars a year.

Honey bees are not native to the Americas; colonists brought them in the 1620s. That makes them a managed tool as much as a wild species, and it is one reason conservation of native pollinators and conservation of honey bees are different problems.

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The waggle dance is the thing no other animal does. A returning forager walks a figure of eight on the vertical comb; the angle of the straight waggling run relative to straight up equals the angle of the food source relative to the sun, and the duration of the run encodes distance, roughly one second of waggling for every kilometre. Nestmates follow the dancer in the dark, read the angle and timing through touch and vibration, and fly to a patch they have never seen. Karl von Frisch decoded the dance and shared the 1973 Nobel Prize for it.

The sensory kit behind that is precise. A honey bee has five eyes: two compound eyes of several thousand facets each, and three simple ocelli on top of the head that track the sun and the sky's polarisation pattern, so a forager can navigate on an overcast day. Its colour vision runs from ultraviolet to orange; it cannot see red, but it sees the ultraviolet nectar guides painted on petals that are invisible to us. The antennae carry around 170 odour receptor types, more than most insects, and bees can be trained to detect single scents in minutes.

Pollen collection is mechanical. Branched body hairs trap grains, and the bee combs them into the corbiculae, the flattened pollen baskets on the hind legs, moistened with nectar. A flying bee carries a positive electrostatic charge that pulls negatively charged pollen onto it before contact. Each trip ends with a few milligrams of pollen or a crop of nectar, and a strong colony stores 20 to 30 kilograms of honey for winter.

Honey Bee

A colony is one queen, a few hundred to a few thousand drones in summer, and tens of thousands of female workers. The queen lays up to 1,500 to 2,000 eggs a day in peak season and lives two to five years. A summer worker lives about six weeks and moves through jobs by age: cleaning cells, nursing larvae, building comb from wax secreted by abdominal glands, guarding the entrance, and finally foraging until her wings wear out. Workers raised in autumn have a different physiology and live four to six months to carry the colony through winter.

Temperature is managed to within a degree. Brood is held at 34 to 35 °C whether the outside air is 5 or 40 degrees: workers fan at the entrance and spread water droplets to cool the comb, and shiver their flight muscles to heat it. In winter the colony forms a cluster that contracts as it gets colder, with bees rotating from the cold outer shell to the warm core.

Reproduction happens at colony level. In spring a strong colony raises new queens, and the old queen leaves with roughly half the workers as a swarm. Scouts search for a cavity, dance for the sites they find, and the swarm commits once a quorum of scouts favours one site, a decision process Thomas Seeley has shown reliably picks the best option available. The waggle dance, in other words, is used for real estate as well as food.

A forager visits 50 to 100 flowers per trip and makes a dozen or more trips a day, and a colony fields thousands of foragers at once. That volume is why honey bees can set a commercial fruit crop in a few days of good weather. Apples, almonds, blueberries, cherries, cucumbers, melons, squash, sunflowers, and canola all depend on or benefit heavily from insect pollination, and in most of those orchards and fields honey bees do the majority of the visits.

In wild and semi-wild habitat the picture is more mixed. Honey bees pollinate many native plants, but they are generalists, and at high density they can compete with native bees for nectar and spread diseases to them. The 4,000 native bee species in North America, and the hoverflies, butterflies, moths, beetles, and bats alongside them, are better pollinators of many wild plants and of crops such as tomatoes that need buzz pollination.

Honey bees are also under real pressure. The parasitic mite Varroa destructor, which arrived in Europe and North America in the 1980s, is the single biggest cause of colony loss; US beekeepers have lost 30 to 40 percent of their colonies in most recent years and replace them by splitting hives. Pesticide exposure, poor forage in monoculture landscapes, and pathogens the mite spreads compound it. Managed colony numbers are stable because beekeepers rebuild them, which hides how hard the system is working.

One forager's discovery becomes the whole colony's flight plan within minutes. That is the honey bee's real superpower.

The dance is a lesson in information design. It carries exactly two numbers, direction and distance, plus a quality signal in how long and vigorously the bee repeats it. Nothing about the flower's colour or the route is encoded; the receiver supplies that. Compact, high-value signals that leave the detail to the person on the ground move organisations faster than exhaustive reports.

The swarm's house-hunting is a lesson in decision-making. No scout sees every option, no bee is in charge, and bad sites lose support because their dancers stop sooner. Seeley's work shows the swarm reaches a correct choice more reliably than most individual bees would, and that is the model behind a good deal of modern research on group decisions.

If you want to watch all of this, you do not need a hive. A patch of flowering plants on a warm afternoon will give you foragers to log, and a known colony entrance will give you the division of labour.

• Honey bee, not wasp

  Honey bees are hairy, golden-brown with dull stripes, and carry pollen on the hind legs. Wasps are smooth, bright yellow and black, with a narrow waist. Hoverflies mimic both but have one pair of wings and hover in place.

• Read the pollen baskets

  The colour of the pollen load tells you what the colony is working: bright orange from dandelion, grey-blue from poppies, pale yellow from fruit blossom. It is a free survey of what is flowering within 3 km.

• Find the entrance

  Watch the direction foragers leave a flower patch; they fly straight home. A column of bees moving in and out of a tree hollow, wall cavity, or hive at a steady rate is a colony. Guards at the entrance inspect arrivals.

• A swarm is not an emergency

  A hanging cluster on a branch in spring is a resting swarm with no brood to defend; it is usually calm and will leave within a day or two. Photograph it from a few metres and report it to a local beekeeper if it is somewhere awkward.

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