Ben Aldiss describes the life cycle of one of the planet's most useful insects
If there is one creature teachers would like their pupils to emulate, the honeybee must be it. And is it any wonder? There is a lot of truth in the saying, "as busy as a bee". Tirelessly buzzing from flower to flower in its unceasing, selfless quest for pollen and nectar, this marvel of evolution keeps going from dawn to dusk. Imagine what we could achieve if children were as highly motivated.
Honeybees are not the only kind of bee. Like wasps and ants, bees belong to that large and successful group of insects known as Hymenoptera. The name means "membranous wings" and refers to the insubstantial nature of the four small wings that do the seemingly impossible job of keeping a bee airborne.
All ants live in colonies and have a complex community structure, but only a small proportion of wasps and bees are social. Of the 250 species of bee in Britain, just 30 are social - the others lead a solitary existence, during which they meet only to mate. The difference between bees and wasps is simple: bees are herbivores, feeding their young on pollen and nectar, while wasp grubs eat freshly killed flies and other insects.
Among our many solitary species, the mining bees are conspicuous as they emerge from their burrows in sunny banks and earthen paths as the first spring sunshine warms the ground and the early flowers open. Our commonest species, the tawny mining bee, is a rich reddish brown colour and quite furry, like a small bumblebee. The female excavates a shaft in the soil, and creates a series of small chambers at the bottom, then stocks it with masses of pollen scraped from the long fringes of hairs on each of her hind legs. She spends the day visiting flowers to gather this protein-rich food and unwittingly pollinates the flowers in the process.
As she goes from bloom to bloom she sips nectar with her pointed tongue and stores it in an expandable part of the gut called the crop or honey stomach. This not only ensures she has enough energy to fuel her busy life, but the excess is later regurgitated into the chamber along with the pollen, to provide enough nutrients for the entire development of the offspring she will never see.
Such mass provisioning marks a crucial difference between solitary and social insects. It has the advantage that the bee needn't expend any energy in caring for its young, but there are huge risks - despite being tucked up in a secure nest chamber, the abandoned grubs must fend for themselves, a flaw that has been exploited by other bees.
Nearly every one of the 60 kinds of mining bee has a sinister alter ego - an unrelated species that watches its every move as it labours to prepare its nest site. The moment a chamber is finished and the mining bee has laid an egg in the mass of pollen and nectar, the so-called homeless bee makes its move. As the mining bee sets off to collect food for the next chamber, the homeless bee darts down the tunnel and deposits its own egg next to that of its host. What happens next is very simple. The egg of the parasitic bee hatches more quickly than that of the mining bee, and the young grub quickly eats the other egg before feasting on the banquet of nectar and pollen. This strategy is hugely successful. Emerging as an adult female the following spring, all the homeless bee has to do is mate, then lie in wait a safe distance from the nest of its host, while the mining bee does all the hard work.
Before your pupils get ideas of transferring this principle to homework, perhaps you should point out that there is always a downside. Whereas the mining bee can shelter in its burrow, the homeless bee is vulnerable to attack from predators, being out in the open all hours of the day and night. Not surprisingly, many are killed. However, evolution has gone some way to minimise the risks. The outer skin - or exoskeleton - of the homeless bee is thicker and harder than that of its host, making it more difficult for the jaws of a nocturnal predator, such as the ground beetle, to penetrate, and it is also more brightly coloured, with bands of black and yellow. This makes the bee look like a wasp, putting off its most likely daytime predators, birds.
Carpenter bees make their burrows in wood, and these include the familiar leafcutter bee. You may be thinking this is not particularly familiar - the bee itself is not very conspicuous - but its handiwork can be seen on any rose bush from June onwards. If you've ever wondered what those neat curved cut-outs in the leaves are, the mystery is about to be solved. Whereas most carpenter bees line their wooden burrows with a sort of saliva that dries to a rice-paper consistency, the leafcutter makes honey-pots out of leaves intricately glued to make water-tight barrels. A stack of six to eight of these is fitted snugly into the tunnel, each having been provisioned with pollen and nectar and provided with a close-fitting lid to protect the developing egg inside. What is so remarkable is the precision with which the bee cuts the leaf to make the sides of each container, having already cut a perfect circle to fit the bottom. An equally perfect circle is used as the lid, so no leakage of the contents occurs.
Bumblebees have been in the news recently, as their numbers have drastically declined in the past few years. This is undoubtedly due to the reduction in wild flowers and the increased use of insecticides on agricultural land. In East Anglia alone, more than 11,000 miles of hedgerows were removed between 1947 and 1985 to make room for more crops.
Not only did this destroy trees and shrubs necessary for mammals and nesting birds, but all the associated flowering plants went too. The situation has now markedly improved and hedges are being replanted, but the position of some of Britain's bumblebees is still precarious.
All our 22 species of bumblebee are social insects, but six of them are parasites, rather like the homeless bees. The common buff-tailed bumblebee begins its life cycle in the early spring when the young fertilised queen emerges from hibernation. She visits the first flowers of the year for nectar on sunny days, sometimes as early as February. Next, she seeks a suitable place for her colony. This is usually underground in the disused mouse or vole nest. Having hollowed out the ball of moss and grasses within, she secretes scales of wax from between the segments of her abdomen, chews them until they are pliable, then carefully moulds them into a large honeypot. Her life gets busier now, as she flies to and fro to collect nectar from tubular flowers with her long tongue. Enzymes in her crop convert the sugars in the nectar to glucose and fructose and she regurgitates the mixture into the waxen honeypot to provide her with reserves of food to tide her over periods of cold wet weather.
As she bumbles from flower to flower, her furry body gets dusted with pollen. Each hair is intricately branched with the express purpose of catching as many grains as possible. As a bee goes about its business, it periodically combs the front of its body with its front legs and the rear with the hind ones. Pollen raked from the fur in this way is then deftly transferred to an ingenious arrangement of bristles on each hind leg called the pollen basket, where it is packed tight with another implement - the pollen press. In this way the bumblebee can carry as much as 60 per cent of its already considerable body weight. On returning to her nest, she kicks off the pollen using her middle legs and uses it to build a ball of food moistened with nectar, which eventually grows to the size of her body, at which point she lays a number of eggs on its surface.
After a few weeks, during which the queen's body heat is used to help speed up their development, the grubs spin silk cocoons, then hatch as worker bees -females like the queen, but smaller and infertile. The workers now take over all domestic and foraging duties, leaving the queen to concentrate on egg-laying. The colony develops into a family of up to 300 individual bees, all of which are female, until the queen's supply of sperm dries up towards autumn. Subsequent eggs are unfertilised and develop into male bees or drones. New queens are also produced at the end of the summer: grubs destined to be queens rather than workers are fed more, so grow bigger.
By the time of the first frosts, the young queens and males have left the nest and mate with others from colonies further afield. The workers and the old queen die, as do the males once they've mated. The newly fertile queens feed on nectar and pollen to boost their fat reserves before finding a cool, dry place in which to hibernate over the winter.
Honeybees are arguably the most advanced of all social insects. In common with bumblebees, the queen is long-lived and the generations overlap. This ensures efficient rearing of young as well as vastly reducing the risks of predation to which solitary bees are prone. But here the similarity ends - honeybees are awe-inspiring in their degree of social structure and efficiency of honey production: they leave bumblebees and wasps in the cold. When Karl von Frisch discovered that they actually communicate, the scientific world was stunned (see box). Are honeybees intelligent? The answer appears to be "no", but they are certainly impressive.
Honeybees evolved in south-east Asia, where their social behaviour enabled them to co-operate so that they were able to store quantities of honey considerably in excess of their immediate needs. This allowed them to radiate far beyond their jungle origins into temperate areas, their stores of honey providing enough food and energy to cope with the worst European winters.
The honeybee's life cycle couldn't be more different from that of the bumblebee. As we've seen, the bumblebee queen awakes from hibernation to weeks of drudgery, until her duties can be taken on by the workers. The honeybee queen lives her entire life at an average temperature approaching that of the human body, but she cannot initiate a colony by herself. She is bigger than the workers, but she has no pollen-collecting apparatus on her legs or wax-secreting glands, and her jaws are not designed for fashioning the intricate hexagonal honeycomb cells.
Honeybee colonies are perennial - and very big. A hive can average 80,000 bees, with the queen laying 2,000 eggs a day. At some point, usually in early summer -the numbers get too big. The workers sense this, as the all-important chemical pheromone exuded by the queen loses its strength.
They then build special wax cells, in which grubs which would ordinarily become workers are fed a special diet. Their rate of growth becomes prodigious, and they soon turn into adult queens. As a colony can only support one, the bees become increasingly excited until the old queen flies from the hive with a cloud of workers, leaving the young queens to fight for supremacy in the diminished colony.
The first to crawl from its silk-capped cell makes a squeaking noise, called piping, which stimulates the others (some as yet unhatched) to do the same. In this way, the superior queen is guided to their cells and stings them in situ, or grapples to the death with her freshly emerged and therefore weaker rivals. The old queen and her escorts swarm on a conspicuous object such as a tree branch until scout bees return to signal the location of a likely nest-site, whereupon they fly en masse to their new home and the cycle begins again.
Nearly all our bees do an invaluable service by pollinating our wild flowers and orchard trees, but honeybees are particularly special. As providers of honey, wax, royal jelly and propolis (resin collected from trees), they take their place as one of the world's most useful domesticated animals.
The Hive: The Story of the Honeybee and Us by Bee Wilson (John Murray, Pounds 14.99)
Field Guide to the Bumblebees of Great Britain and Ireland; by Mike Edwards and Martin Jenner (Ocelli pound;9.99)
Bumblebees by Christopher O'Toole (Osmia pound;4.95)
* The British Beekeepers' Association (lists county association members, often willing to send representatives to schools): www.bbka.org.uk
* English Nature feature on bumblebeeswww.english-nature.org.uk newsstory.asp?ID=468