Bombus terrestris (Buff-tailed bumblebee) on flower iStockphoto / Zhikuang

Bumblebees don't play well with others and certainly don't want young upstarts barging in on their favourite foraging routes, researchers from Queen Mary University of London have found.

The team's study, Monitoring Flower Visitation Networks and Interactions between Pairs of Bumble Bees in a Large Outdoor Flight Cage, examines how interaction between bumblebees affects the way they plan their routes between flowers.


Lead author Dr Mathieu Lihoreau said that "like other pollinators, bees face complex routing challenges when collecting nectar and pollen -- they have to learn how to link patches of flowers together in the most efficient way, to minimise their travel distance and flight costs, just like in a traveling salesman problem."

To date, little research has been done on how the interaction of bumblebees on flowers affects the routes they choose, for example whether less experienced bees copy those who've already established routes.

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The Bombus terrestris bees were released into an 880m2 outdoor flight cage, which contained 10 artificial flowers -- feeding stations that dispensed a sugar solution -- at various distances from one another and motion-detecting webcams to monitor the bees, which were marked with individually numbered tags positioned on their thorax.

First, after several bees had been trained to use the flowers, one bee was given the opportunity to familiarise itself with its surroundings in 25 consecutive foraging sessions. Then a second bee was released into the area so that it could forage alongside the established resident for another 25 bouts. By the study's definitions, "a foraging bout started when the forager left the nest and ended upon its return to the colony."


Co-author Professor Lars Chittka said that "we wanted to monitor the way bumblebees behave when they bump into each other at flowers -- would they compete, attack each other, or tolerate each other?"

They found that, if two bees landed on the same flower, they'd only feed together 6.3 percent of the time -- the other 93.7 percent of encounters resulted in the bees trying to push each other off the platform using their head or legs, ending in one or sometimes both leaving the feeding platform. However, the team noted that "bees were never observed to bite or sting each other."

Although "inexperienced bees discovering a new foraging environment tend to copy the flower choices of other foragers to identify the most rewarding flowers" -- using olfactory markers, rather than visual cues, to tell where the other bee had been -- they were typically met with hostility, and the established resident bee was more likely to start an engagement than the newcomer. Resident bees tended to maintain their existing foraging areas by more frequently visiting familiar flowers and kicking out newcomers when they found them.


By contrast, in the rare instances when newcomers evicted established bees, they "prioritized revisits to flowers from which they had successfully evicted residents and obtained a nectar reward, presumably to establish their own foraging area." This resulted in an overlap between the bees' foraging areas as a result of competitive interactions.

Resource depletion was also a key factor in the bees' behaviour, causing experienced bees in particular to extend their range to include other flowers when nectar supplies along their route were depleted.

The team concludes that "these interactions may favour spatial partitioning, thereby maximising the foraging efficiency of individuals and colonies," so the bee-on-bee tussles ultimately mean that colony as a whole makes the most effective possible use of the flowers in its vicinity.