Garden blogs

Where are all the bees?

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In the UK we have over 270 species of bee (1 of which is the honeybee, 24 are bumble bees, and the remainder are solitary bees). Bumble bees and honeybees are both eusocial and therefore live in large communities of individuals ruled by one fertile female (the queen). Most other bees, including leafcutter bees and mason bees are solitary – meaning every female is fertile and inhabits a nest she creates herself. The nests of solitary bees therefore lack queens and workers. There are some exceptions to this rule though, as bees in the genera Lasioglossum and Halictus can exhibit primitive eusocial behaviour where non-reproductive females assist a reproductive female. Hibernation of bees varies from species to species, however, here is a look at the general lifecycle of each group.

Bumblebees

Come the end of summer/early autumn, a mated queen will feed intensively on pollen and nectar and store it as fat. She then spends the winter alone, underground and buried in soil, using up her energy reserves until awakened by warmer temperatures in early spring. Once emerged, the queen will forage for nectar and search for a suitable nesting site to spend the year. Bumblebees can nest underground in old burrows or above ground in used bird boxes, holes in trees or roof cavities.

Upon finding a suitable nest, the queen creates a ball of pollen moistened with nectar which she lays fertilised eggs on. She also creates a pot made of wax to fill with regurgitated nectar (honey) which she drinks from as she incubates her eggs. After several days, the eggs turn into larvae and can be left as the queen undertakes foraging trips to collect pollen and nectar. During each foraging trip the brood will cool down and so it is vital that the nest is located close to rewarding flowers. After around two weeks, these fertilised eggs will develop into adult worker bees (females). The queen only supplies food for her first one or two broods, after which the worker bees take over the role of foraging. The queen remains inside the colony, laying eggs and caring for larvae. A bumblebee colony typically contains 50-400 workers.

During late summer a ‘switch-point’ is reached and the queen begins to lay unfertilised eggs which give rise to males, a specialised phenomenon observed in many insects known as haplodiploidy. Male bumblebees leave the nest as soon as they emerge and will not return. They spend their time near flowers, foraging for nectar and waiting for a mate. Some workers are also able to lay unfertilised eggs, but the queen prevents this with physical aggression and pheromones. Workers will also eat or remove nearly all eggs laid by other workers (known as worker policing) which means that the queen is the mother of all individuals in the colony at this stage.

Once the male eggs are laid, the remainder fertilised eggs are fed more than previous broods, and these give rise to new queens. The original queen then loses her ability to suppress worker reproduction and the workers begin to lay eggs which develop into males. This creates worker-queen conflict which can force the old queen to flee the nest. New queens leave the nest to find a mate before storing up on pollen and nectar for the long winter ahead. Eventually the original queen will die along with her sons and workers as the frost appears.

In southern England particularly, some species of bumble bees have been observed foraging during the winter. This means that new queens are creating new nests instead of hibernating, due to warmer temperatures. Winter flowering plants such as mahonia are very beneficial during this time for providing forage. You can record your sightings of winter-active bumblebees here.

Honeybees

Honeybees have a similar social system to bumblebees but colonies are much larger and are usually managed by humans in hives to produce honey, however, feral colonies can exist in the wild. One colony can contain tens of thousands of workers and up to a few thousand male bees (drones), along with a queen.

Honey is the main food store that they rely on during the cold winter months, however, pollen is also used as a source of protein. If provisions are too low, then a colony can freeze to death. Once the summer is over and the temperature starts to decrease, the rate at which the queen lays eggs decreases, and the workers focus on keeping the colony warm. Before winter, drone bees are expelled from the hive as they are now useless to the colony however, they cannot forage for themselves, so they soon die.

During this time, colony activity is very low however if there are warm winter days, workers can leave the hive to obtain fresh nectar. From mid-winter onwards, the queen will begin laying eggs again, peaking during late spring. She can choose whether to lay fertilised or unfertilised eggs, which develop into workers and drones respectively. The sole purpose of a male honey bee is to mate with a queen during her ‘virgin flight’, after which they will die.

The lifecycle of honeybees is much more complex than bumble bees as they tend to survive year after year if populations are healthy and are intensively managed by humans. A queen honeybee can live for three to four years but is usually replaced after one or two.

Solitary bees

Solitary bees are more variable between species when it comes to hibernation. Most adults will die before the winter comes, having left their eggs in a safe space with stores of pollen and nectar. Solitary bees that emerge in the spring (e.g. red mason bee, Osmia bicornis) will develop over the summer from an egg to a young adult, spending the winter waiting for the temperature to increase so that they can emerge. Those that emerge later in the year overwinter as larvae and grow very little, completing their lifecycle during the spring (e.g. leafcutter bee, Megachile willughbiella)

Very few solitary bee species can overwinter as adults in the UK and are mainly confined to the southern counties (some Lasioglossum and Halictus species). These will mate in the autumn and females will hibernate underground, emerging in the spring to lay eggs.