Pollination

Pollination is how flowering plants reproduce. It is the transfer of pollen (a powdery yellow dust containing male plant cells) from the male parts of a flower to the female parts of a flower of the same kind. Plants cannot move themselves, so they need help. Most use animals (especially bees, butterflies, birds and bats), while some use the wind. Without pollination, most plants could not produce seeds, and the planet would look extremely different.

• Main pollinatorsBees, butterflies, moths, birds, batsPlus the wind and a few small mammals
• Bee speciesapprox. 20,000Of which the famous honey bee is just one
• Flowering plants needing pollinatorsapprox. 87%Most species depend on animals to pollinate them
• Food crops needing pollinatorsapprox. 75%Including most fruits and many nuts and vegetables
• Bees' favourite colourBlue, purple, ultravioletBees cannot see red, but can see UV
• Pollen grains per flowerUp to several millionA single anther holds thousands

How pollination works

A flower's male parts (the stamens) produce thousands of tiny pollen grains. Each grain contains the plant equivalent of sperm. For a seed to form, a pollen grain has to reach the female part of a flower (the stigma) of the same kind. The grain then grows a long tube down through the flower to fertilise an ovule in the plant's ovary, and the fertilised ovule starts growing into a seed.

For most plants, the trick is just getting the pollen from one flower to another. Plants have evolved many clever methods.

The biggest pollinators: bees

Bees are the most important pollinators by a long way. There are about 20,000 species of bee in the world, of which the famous European honey bee is just one. Bumblebees, solitary bees, mining bees, mason bees, leafcutter bees and many more all do important pollination work.

Bees visit flowers to collect nectar (a sugary liquid) and pollen (a high-protein food). As they crawl around inside the flower, pollen sticks to their fuzzy bodies. When they fly to the next flower, some of that pollen brushes off onto the new flower's stigma. The bee gets food; the plant gets a free delivery service.

Other animal pollinators

Many animals besides bees pollinate plants.

• Butterflies and moths: long thin tongues let them sip nectar from deep tubular flowers. Many moth-pollinated flowers are white and open at night.
• Hummingbirds and sunbirds: hover in front of flowers, dipping their long beaks in for nectar. Many bird-pollinated flowers are red (because birds can see red, but most insects cannot).
• Bats: in the tropics, fruit and nectar bats pollinate large pale flowers that open at night, including the famous saguaro cactus and many tropical fruit trees.
• Beetles: pollinate magnolias, water lilies and some of the most ancient plant species.
• Flies: pollinate many smelly or strange-looking flowers. Some orchids even mimic rotting meat to attract flies.
• Small mammals: a few mice, lemurs and even primates pollinate certain plants.

Wind and water pollination

Not every plant uses animals. About 10% of flowering plants and almost all conifers use the wind. Wind-pollinated plants make huge amounts of small, light pollen that floats easily on the breeze. They tend to have small, plain flowers without bright colours or scent (no point attracting insects if you do not need them). Grasses, oaks, birches, hazel and most cereal crops are wind-pollinated. Wind-pollinated plants are responsible for almost all hay fever.

A few aquatic plants are even water-pollinated: they release pollen into the water, which drifts on the currents until it finds another flower of the same kind.

Why pollinators matter for us

Pollinators are not just important for wild plants; they are essential for human food. Around 75% of the world's food crops depend on animal pollination to some degree. This includes most fruits (apples, strawberries, blueberries, oranges, watermelons), most nuts (almonds, hazelnuts, brazil nuts), many vegetables (tomatoes, courgettes, pumpkins) and crops like coffee and chocolate.

Without pollinators, supermarket shelves would look very different. Some crops would disappear completely; others would become rare and expensive. The total value of insect pollination to global agriculture has been estimated at over $500 billion per year.

Fact Bees can see ultraviolet light, which is invisible to humans. Many flowers have hidden ultraviolet patterns called "nectar guides" that act like landing strips, leading bees straight to the centre of the flower where the nectar is. Photograph a flower with a special UV camera and you can see these striking patterns yourself.

Why pollinators are in trouble

Around the world, populations of bees and other pollinators have been falling for decades. Threats include:

• Habitat loss: the loss of wildflower meadows, hedgerows and other natural areas to farmland and roads.
• Pesticides: especially a group called neonicotinoids, which are harmful to bees even in tiny amounts. Many of these are now banned in the EU and UK.
• Disease and parasites: especially the Varroa mite, which has wiped out countless honey bee colonies worldwide.
• Climate change: pollinators sometimes wake up too early or too late and miss the flowers they normally pollinate.

The good news is that you can help. Planting a wide range of flowering plants in your garden, avoiding pesticides, leaving wild corners and providing bee hotels can all support local pollinators.

Did you know? One of the world's most expensive foods, the spice vanilla, has to be hand-pollinated. Vanilla orchids were originally pollinated only by a particular Mexican bee. When farmers tried to grow vanilla elsewhere in the world, the plants flowered but never set seed. Today almost all commercial vanilla is pollinated by people working flower by flower with a tiny stick, which is one of the main reasons vanilla is so expensive.

Deeper dive: how flowers and pollinators co-evolved

The partnership between flowering plants and their pollinators is one of the most successful examples of co-evolution in nature. Each side has shaped the other over the past 140 million years, ever since the first true flowers appeared.

Flowers that get pollinated more efficiently produce more seeds and more offspring. So natural selection has favoured flowers that are more attractive to the right kinds of pollinator: brighter colours, sweeter nectar, more perfumed scent, easier-to-reach pollen. In turn, pollinators that are more efficient at visiting flowers get more food and produce more offspring, so they have evolved features that let them get the best of any flower: longer tongues, bigger eyes, the ability to fly hovering, the ability to remember where the best flowers are.

The result is some extraordinarily tight partnerships. The star orchid of Madagascar has a nectar tube about 30 centimetres long. Charles Darwin saw one and predicted that there must be an as-yet-undiscovered hawk moth on Madagascar with a 30-cm-long tongue to pollinate it. Critics laughed. Forty years later, in 1903, scientists found exactly such a moth, with exactly that tongue length, pollinating exactly that orchid. Co-evolution had produced a partnership so specific that one species literally could not exist without the other.

The rise of flowering plants and pollinators between 140 and 100 million years ago is one of the great events in the history of life. It transformed almost every ecosystem on Earth and helped create the diverse, colourful world we know today.

For more on flowers, see flowering plants. For the full sequence from seed to seed, see plant life cycle.