On one of the warmer mid-spring days invigorating the Norfolk Broads this year, a decidedly hairy bee emerges. She is a Buff-tailed Bumblebee Bombus terrestris. The bee forages hungrily on flowering pussy willow before beginning her search for a nest site. Many other bumblebees feed around her and she feels a bit cramped. Queuing up for pollen at this stage of the season does not bode well for her future offspring. She will soon lay many hundreds of eggs in her nest but is already sharing the willow with many of her sisters, born in the same colony as her the previous year. The proximity of other individuals and fellow Queens forces her into a drastic decision: taking one last sip of nectar she buzzes over shingle beaches and out over the cold North Sea.
Flying east, she determinedly barrels her way through buffeting winds until, almost 130 miles later, she spies the coast of the Netherlands.
This spring, on 9th April 2016, there was someone watching as she made landfall. A naturalist enjoying the coast and watching bird migration noticed a bumblebee flying in from the sea, and not just one, with her he counted 3,387 other miniature furry projectiles flying en-masse towards their grassy target. Once the Queens arrive they disperse to find suitable nest sites with less competition and a greater distance between the colonies of related bees than back home where they were born.
3,387 is a large group, but by no means the only group to make the journey. Groups of bees of varying size are a normal sight along the coast of Holland at this time of year, arriving from across the sea in places like the Nordkaap Reserve in the northern Netherlands. No one really knows why these huge bumblebee Queen migrations occur in the springtime but it has been postulated that it has something to do with the Queen’s need for dispersal. Flying far from your original nest site reduces the risk of your daughter Queens mating with males closely related to them, and thus increases the genetic diversity of the population. The actual path the bees follow is potentially also one of ancestral memory. Eight thousand years ago the seas were lower and a land bridge was present across the North Sea, connecting the UK to Continental Europe. This potentially means that bees originally used this route for dispersal but as sea levels rose they had to fly a little further each time! No records of any return migration have been recorded and so it is not inconceivable that this is just a one-way migration route at the beginning of the year due to the success of the Buff-tailed Bumblebee populations in the east of England.