Nature on our doorsteps - ‘Winter-active’ bumblebees

By Rosaleen Dwyer

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into the natural heritage around us and the beautiful biodiversity of the plants and creatures

It was always accepted that the normal lifecycle for Irish bumblebees involved colonies dying away before winter, with only newly-mated queens surviving.

Queens would then hibernate over winter, emerging in springtime to start new colonies.

Flowering shrubs like Mahonia offer vital food to active bumblebees in winter compressor

Flowering shrubs like Mahonia offer vital food for active bumblebees in winter

Queens might occasionally be spotted during winter, disturbed from hibernation by an unusual mild spell and hoping to find nectar and pollen in an early-flowering dandelion.

Surprisingly, worker bumblebees are now also sometimes seen visiting winter-flowering plants like heathers, Mahonia, and Hebe shrubs.

This suggests that some colonies are in fact surviving over winter. These sightings are mostly of workers of the Buff-tailed Bumblebee, with the cream-coloured tail.

The reason behind this unusual ‘winter-active’ behaviour is not very clear, and experts are not yet sure if it will pose a long-term problem for these insects.

Buff tailed bumblebees are more normally spotted in summertime compressor

Buff-tailed bumblebees are normally spotted in summertime

The question of climate change is of course raised. Milder winter weather may indeed allow some colonies to continue but these would be at risk if colder spells occur, killing off whole colonies including immature queens.

There is a possibility too that these winter-active bumblebees may in fact be a different sub-species of the native Irish Buff-tailed Bumblebee, perhaps arrived from overseas.

 DNA investigations of these winter-active individuals may help to find an answer to this unusual bumblebee behaviour.

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