Male bumblebees seek mates on the hills

White-tailed bumblebee (c) Dave Goulson Males spend their lives drinking and looking for mates

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Bumblebee males head for the hills to find mates, according to scientists in Scotland.

Researchers made the discovery while investigating how bees are distributed across their habitat.

The behaviour, called "hilltopping", has been observed in butterflies in the past, but not in bees.

Little is known about how bumblebees find their mates and mating itself is rarely observed.

Professor Dave Goulson from the University of Stirling became interested in the distribution of bumblebees when he encountered so many in his local area.

On a regular run with co-workers in the hills next to the campus, Prof Goulson noticed an abundance of the large, fuzzy pollinators.

This casual observation led to a scientific investigation into what he thought was an unusual distribution of bees in the windswept, flowerless habitat.

Start Quote

It's quite a neat, simple 'dating' mechanism for butterflies but nobody knew that bees did it”

End Quote Professor Dave Goulson University of Stirling

The study, published in the journal Ecological Entomology, revealed that it was male bumblebees from four species that were most frequently found on hilltops.

"Male bumblebees are essentially lazy," explained Prof Goulson.

"You can see gangs of them sitting around on flowers in July and August and, in between drinking, they go looking for mates."

With a reduced amount of plants suitable for foraging at the top of the hill, Prof Goulson proposed that the bees favoured location was solely a mating strategy.

The bumblebee expert compared his findings to those of previous studies on hilltopping behaviour in butterflies, flies, and wasps.

Scientists studying these insects found that males and females seeking mates flew to the tops of hills to improve their chances of reproducing.

"It's quite a neat, simple 'dating' mechanism for butterflies but nobody knew that bees did it," said Prof Goulson.

Secretive sex lives

For bumblebees it seems that only the males make the effort to be seen.

INTELLIGENT INSECTS

Although his results showed males congregating on hill tops, Prof Goulson did not record any females taking advantage of the gathering.

The striking insects are surprisingly mysterious and their behaviour, and particularly their reproductive strategies have been the subject of study for many years.

In the late 19th Century, Charles Darwin studied the flight paths of male bumblebees in his garden and found that they left pheromone markers along a regularly patrolled circuit.

But no observations have since been made of females reacting to these signals.

"There are some well-known things that male bumblebees do that have always been assumed to be something to do with how they find mates," Prof Goulson told BBC Nature.

"But none of them are terribly well understood because you almost never see [the bees] actually mating."

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