Pollinators in Britain

Pollinators are animals that transport pollen grains from the male anther of a flower to the female stigma of another flower in the process called pollination. Click HERE to learn more about pollination. In Britain most pollen transport is carried out by insects but many trees and grasses rely on wind pollination. Worldwide 87% of flowering species are pollinated by animals with 65% by insects.  In the tropics birds, bats and some mammals are important pollinators. 

Pollinators such as bees, butterflies, moths, wasps, beetles and flies pollinate flowers in Britain. Some of these insects are generalists but others are closely adapted to feed on certain flowers. Here we describe  the insect pollinators and what they feed on.

Bees are the most important pollinators of flowers in Britain, primarily because they feed on and store both pollen and nectar. Bees collect pollen on their bodies as they forage. Some transfer the pollen to special baskets on their hind legs, as shown in this photo. Pollen contains proteins needed for larval growth. They use nectar as a water or energy source or store it as  nectar or honey for  later use.  Bees have a proboscis which includes  a hairy tongue that can be used to lap up nectar or honey as it is pushed in and out. The proboscis swings back under the head when not in use. Honey bees have mid-length tongues (6mm) and some bumble bees have long tongues (10 to 19mm) so they can reach the nectar in nearly all flowers. Bee’s eyes have 3 photoreceptors – ultra-violet, blue and green, which compares with humans red/blue and green. So bees can’t see red (it appears as black) but can see UV. Bees see purple/violet and blue best but can see yellow/orange flowers. In Britain there are 270 species of bee of which about 250 are solitary. The rest live in groups and are termed social bees and include 18 species of Bumblebees (genus Bombus) plus 6 cuckoo bumblebees that parasitise Bombus nests and one species of Honey-bee Apis melllifera. All bees, except the honey bee,  have annual life cycles.

Social Bees (a) Bumblebees have an annual life cycle.  In autumn the colony disintegrates and the old queen, females and males die. New queens, produced and mated in late summer, search for a hibernation site and don’t emerge until early spring. After feeding, the queen searches for a safe site for a new colony. Bird boxes, thick grass, hedge bottoms or lofts are typical sites. The queen then founds a new colony by creating wax cells to hold pollen or honey. The honey pots are used to store regurgitated nectar. The queen then lays eggs in the pollen pots. The queen holds sperm collected last summer.  The queen controls whether the eggs are fertilised (to produce females and future queens)  or unfertilised (to produce males). Females are produced first and they go out and forage for nectar and pollen. The colony expands and may reach from 50 to 400 bees. Towards midsummer the queen produces males and some larvae that will develop into new queens. Then the males leave the colony and new queens emerge and mate. Queen bumblebees pollinate early flowering plants such as Hellebore.

Social Bees (b) The Honey Bee (Apis mellifera)  is native to Europe, the Middle East and Africa but has been domesticated for centuries as a provider of honey. Honey bee colonies  can persist for years.  Each colony has a queen, worker bees and drones. Colonies can have up to 80,000 bees. The queen is held within a brood chamber and  lays 1000 or more eggs per day, each one into a hexagonal cell. Each egg produces a larva. Foraging worker bees collect and store  pollen and honey (produced from nectar). They forage selectively for nectar or pollen as required by the hive. Stored pollen and honey is eaten by worker bees to produce ‘bee bread’ which is fed to larvae to produce female workers and male drones. The queen’s life span is 2 to 7 years. Virgin queens are produced when the queen’s egg production decreases. They fly out of the hive to mate and return to replace the old queen.  Honey bees need to store 14 kg of honey to maintain temperature and survive winter. A strong colony can produce 2-3 times more than it needs and this is sold commercially by beekeepers. Honeybees  are also bred as crop pollinators in the USA, where millions of hives are transported long distances  to pollinate crops such as  Almonds in California.

Solitary bees. In the spring males, then females, emerge from a nest. The males mate with the females immediately and die. The females then excavate nests which could be underground or aboveground. In other species such as the Mason bee, shown here, they use existing cavities. The female moistens the cavity with nectar, adds pollen and then lays a female egg on it, before sealing it with mud. In the same cavity she adds a series of male eggs.  The eggs hatch into larvae. After 6 weeks the larvae pupate but do not emerges until next spring. Females finish nest building in summer and die.  

Butterflies and Moths visit flowers to collect nectar. They feed by sucking nectar through a proboscis which is coiled before use but may be extended to 18mm in butterflies (photo below) and 75mm in the Convolvulus Hawk-moth. They collect pollen on their proboscis, legs and body whilst feeding on nectar. Butterflies and Night-flying Moths are attracted to scented flowers such as Honeysuckles, Pinks, Hyacinths, Lilacs and Buddleia and have a preference for certain colours but scent, ease of access to nectar, colour and shape of flower may all be interlinked when choosing which flowers to visit. White flowers may be easier to see at dusk. Hawk-moths can hover while feeding so, can quickly sample individual flowers on the head  of, for example, Red Valerian.

Flies – there are over 5000 species of true flies – called diptera because they have only 1 pair of wings. They are important pollinators of flat or bowl-shaped flowers with well-exposed nectar. Hoverflies are true flies They are attracted to flowers of the Aster family which have compact, flat heads. There are 280 species in Britain. They feed on pollen and nectar. Rhingia hoverflies have long mouthparts and feed on nectar in tubular flowers. The proboscis is normally 2 to 4mm but in Rhingia it is 7mm plus. Hoverfly females lay eggs which hatch as larvae, then pupate and become new hoverflies. The larvae are predators often feeding on aphids. Hoverflies are not social. Adults feed on nectar, honeydew produced by aphids and pollen which, unusually for insects,  they can digest and provides a protein-rich source for their eggs. Hoverflies are important pollinators of oilseed rape. They are also effective pollinators of commercial strawberries. The Beefly is a pollinator of early-flowering species such as the Primrose. Its proboscis is up to 7.5mm long.
Beetles  have few adaptations that enable them to be efficient pollinators but they visit flowers in large numbers.  Some species eat flowers but some are pollen eaters whilst others pollinate flowers by accident. Magnolias have long history of  pollination by beetles. They are attracted to the flower by sweet-smelling secretions and may shelter and feed in the centre of the flower for several hours. If the anthers release pollen during this time, the beetle gets contaminated with pollen grains. Eventually the inner tepals open and release the beetle which then flies off to other trees and pollinates them.

Wasp’s eyes have similar photoreceptors to bees and so do not see red colours. Some flowers such as Figworts  and Helleborines are pollinated by social wasps. They are both late flowering and may attract wasps by their smell. Wasps eat insects and capture insects on which they feed their young and so do not collect pollen but do feed on nectar.

Social wasps are in the Vespidae family with 8 species in Britain. Larvae feed on insects, caught and chopped up by female workers. The nest is built by a fertilised queen, initially with 10 to 12 hexagonal cells. Larvae hatch into female workers which continue the nest building. Males are produced at the end of the summer. Young males leave the colony to try and mate with new queen wasps after which they die off. From late autumn all the unmated females die off. The mated female then hibernates. Hornets are social wasps.

Solitary wasps typically build mud-like structures on the side of walls in which they lay a single egg. Some solitary wasps build a nest but some lay their eggs on paralysed prey. Some solitary wasps prey on honey bees which they capture in flight, paralyse and then push into the single cell of a nest, before laying a single egg in it. The egg hatches and the larva eats the honeybees and then pupates.