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.
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.
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.