What does climate change mean for bumblebees?

This summer has seen yet another record-breaking year in terms of temperature in the UK. Climate predictions suggest that extreme weather events, such as heat waves, are only going to increase, so it’s now more important than ever to consider how climate change will influence wildlife.

The potential impacts of climate change on some animals are well documented. Melting sea ice reduces available habitat for arctic animals such as polar bears and walruses. Ocean acidification, as a result of rising temperatures, can lead to coral bleaching and habitat loss for 1000’s of marine animals.

The negative impact of climate change on these species is clear.

Bumblebees however, are synonymous with the British summer, so surely hotter temperatures will not impede these humblebees?

The tree bumblebee (Bombus hypnorum) first arrived in the UK in 2001, and is now found as far north as Scotland, and has recently been spotted in Ireland. Whether climate change has allowed this bee species to move further north or not we do not know, although increasing temperatures are certainly not stopping this bee from expanding its range.

Most bumblebees are not great in the heat. The fluffiness that makes them so appealing to us has evolved to keeps them insulated in cooler temperatures, and so you could say that bumblebees are always wearing a coat. Not exactly ideal in a heat wave.

Some bees, like the tree bumblebee, seem to be doing fine. However, a paper published in Science in 2015 examining long-term data from 110 years in Europe and North America, found that bumblebees in southernly locations have smaller ranges than before and appear to be moving towards higher altitudes to avoid rising temperatures1. Species that become more range restricted are more vulnerable to extinction. If bumblebees cannot move further north in response to climate change then this is worrying for bumblebee conservation.

Furthermore, it’s possible that climate change could effect the time that flowers and bees are present. For example, some flower species could bloom earlier in the season then they have done historically. Different flower species bloom at different times throughout the year, so it’s possible that generalist bumblebees (those that collect nectar and pollen from a wide variety of different flowers) might be okay in this changing floral marketplace. Other bumblebees however are more specialised and will only feed from a few types of flowers. If there is a mismatch between the timing of these bumblebees and the flowers that they depend on, then this is likely to end badly for both bee and plant.

Could bumblebees modify their behaviour to nullify the impacts of climate change?

If bumblebees that have co-evolved to feed on a certain flower species are unable to do so because of climate change, they could in theory feed on other flowers. However, it is likely that they will be outcompeted by other bees that have already evolved to occupy this niche. Bumblebees that can find flowers will typically forage in the morning and afternoon, when temperatures are cooler and they are less likely to be outcompeted by other bees, such as honeybees. Despite this, rising temperatures could result in other bees, such as honeybees, changing their foraging habits. This could increase floral competition between species.

Despite all of this, with a few noticeable exceptions1–3, we don’t really have a good understanding of how climate change will influence bumblebees, or any bees for that matter. It is likely there will be winners and losers.

As with many other animals, it seems likely that we won’t know what the true impact of climate change on bumblebees will be until it’s too late.

References

1. Kerr, J. T. et al. Climate change impacts on bumblebees converge across continents. Science 349, 177–180 (2015).

2. Bartomeus, I. et al. Climate-associated phenological advances in bee pollinators and bee-pollinated plants. Proc. Natl. Acad. Sci. (2011). doi:10.1073/pnas.1115559108

3. Kudo, G. & Cooper, E. J. When spring ephemerals fail to meet pollinators: mechanism of phenological mismatch and its impact on plant reproduction. Proc. R. Soc. B Biol. Sci. 286, 20190573 (2019).