Life of the Bumblebee
The first bumblebee queens will emerge from hibernation in spring, some as early as February or March. Only the fattest queens survive, they have been hibernating since the end of summer some eight months before emerging. They now need to find the first early spring flowers to feed on as their fat reserves are very low. The pussy willow is an early flowering tree, the female tree produces sugar rich nectar and this is one of the plants the queen will feed on. The male pussy willow produces bright yellow pollen bearing catkins and this is the plant the queen will feed on next. She will stock up on the protein rich pollen to expand her ovaries and to develop their eggs. Sperm is also stored inside each of the ovaries from the summer mating of the previous year. The queens will slowly fatten and the eggs develop inside her. She will now begin to find a nest.
Many bumblebee species like to nest underground, looking for existing holes like a mouse hole. They do need to insulate the nest and will use dried moss, grass, hair, feathers, which will be rearranged into a ball with a hollow centre. Different species of bumblebees nest in different places. Buff-tailed bumblebees like to nest under pavements, concrete, or use airbricks to gain access into the wall cavities of houses. White-tailed bumblebees like to be under the wooden floors of garden sheds. The Early bumblebee may nest in old bird nests, both Early and Red-tailed bumblebees will use bird boxes with old nesting material in. The Tree bumblebee always nest in holes in tree trunks and bird boxes. The Carder bumblebee nests above ground in grass tussocks or under dry leaves in bramble thickets.
The nest will be a loose ball of insulating material with an inner cavity with a hole which the queen can crawl through. This cavity will be about the size of a tennis ball and in here the queen will construct a cup from wax which she will fill with honey. The wax is produced from special glands on the underside of the body, this is then moulded into shape with her mandibles and legs. Pollen is formed into a small ball about the size of a pea, using honey to hold it together and then coated with wax. When the queen is ready to lay eggs, she fertilises them with the stored sperm as they pass out from her body. She will then make a small hole in the pollen ball, pushing a batch of 16 eggs into it and then sealing the hole with wax. Each ovary (which there are 2) can produce 8 eggs at a time. The eggs are shaped like very small sausages and are cream in colour.
The queen will incubate the eggs by holding onto the pollen ball and shivering, this will warm the eggs and keeps them at about 30 C. A lot of energy is used by shivering, this why she has her honey pot in easy reach. This will only last for a little while, so she will need to leave the nest to collect more nectar or she will starve. But if she leaves the nest for too long the eggs and brood will get cold. This will result in the brood developing slowly and she will wear herself out in the search for food.
Plenty of nectar rich flowers need to be close by, a queen will need to visit up to 6,000 flowers to replenish her body weight in sugar each day to incubate her brood. After about 4 days the eggs hatch into comma shaped grubs, with a mouth at one end and an anus at the other. They cluster together eating the pollen dough and as this is used up the queen will need to collect more. The grubs will shed their skin as they grow and will eventually spin themselves a cocoon using silk produced by glands in their mouth. Inside the cocoon they shed their skins again and will resemble an adult bee. This will take about 2 weeks, the emerging bees will be white for a few days and are all female workers.
These workers will remain in the nest and help raise the next batch of brood. Once the workers have developed their adult colours some will start to gather food. The queen will now stay in the nest and be fed by the workers. The first flight out for the workers will be short as they need to orientate themselves with the location of the nest. Once they have perfected their skills in collecting pollen and honey, food will quickly build up in the nest. The queen will lay eggs more rapidly and the numbers of workers will increase. The workers can also produce wax and will build more honey cells. Some species of bumblebee also build cells to store pollen in.
About July the nest has built up to contain maybe as many as several hundred workers. The queen will stop producing a pheromone which tells the grubs to become workers. She starts to produce male and female eggs. The female grubs will become queens and are bigger in size than the workers. The males are smaller, a similar size to the workers. The queen can control the sex of her offspring, fertilised eggs become females and unfertilised eggs become males. The young queens and the males will feed on the honey, and pollen stores before leaving the nest.
The only role of the male bumblebee is to mate, he may mate more than once. He will also not survive the winter. The queens in most species will only mate once and this is soon after leaving the nest. The sperm is stored to be used in the spring when she starts to build her own nest. These young queens will now be looking for a site to hibernate in, this will be just a few centimetres under the ground in loose soil.
Back in the old nest the workers are not being replaced as the old queen is now failing. The food stores have gone into producing new queens and males, by September the nest is empty of any live bees. Early Bumblebee queens will hibernate in June, other species hibernate in July or August. The fat reserves on the new queens must keep then going till spring, some will not survive. In damp weather the queens can get mouldy, or they may drown in wet weather. The surviving queens will make their way out of the soil and into the light on a warm spring day.
The Bumblebee year will start all over again.