UK bumble bee population trends: Common species do better than rarer species

Common Carder bee, Bombus pascuorum, carding hairs from a dead-nettle. / Richard Comont

Data collected by bumble bee Conservation Trust (BBCT) volunteers to assess the country’s changing bumble bee populations have been analyzed in a new way for the first time at the University of Kent – and show mixed results about their decline, with cause for concern for two species.

Data was analyzed for the five commonest species in the BBCT’s BeeWalk dataset. The two rarest species (Early bumble bee Bombus pratorum and Red-tailed bumble bee B. lapidarius) out of the five have declined since 2011 while the two commonest ones (Common Carder bumble bee B. pascuorum and Tree bumble bee B. hypnorum) have increased. The Tree bumble bee, first found in the UK in 2001, has spread rapidly across the country.

Britain’s 25 bumble bee species are some of the nation’s favorite creatures and are also vital for the pollination of crops, garden plants and wildflowers. However, they have suffered huge declines over the past century: two species went extinct in the past 80 years, and eight species are endangered. These species were known to have declined in distribution over the long term but little was known about how bumble bee populations have changed more recently.

Hundreds of BeeWalk volunteers together walked nearly 5,000 kilometers each year to gather information about the numbers, species and caste (queens, workers or males) of the bumble bees they saw and identified.

Statistician Dr. Eleni Matechou, of the Statistical Ecology at Kent group in the School of Mathematics, Statistics and Actuarial Science (SMSAS), devised new methodology to analyze the data collected by BeeWalk. The new statistical methodology uses the UK-wide aggregate data on bumble bee detections and provides important information on each of the bumble bee species, such as the average number of worker and queen bumble bees produced from each nest per year.

Dr. Matechou says, “Volunteers do an impressive job at detecting bumble bees on their surveys and identifying their species and caste, when possible. The data collected so far have provided us with invaluable information on the state of UK bumble bee populations. However, if we had better data, we could decrease uncertainty around our estimates of population trends. We hope we can move this research forward by developing a dedicated BeeWalk smartphone app to help volunteers carry out their work thereby collecting even better-quality data and creating a new class of more sophisticated statistical models to analyze them.”

Reprinted and slightly edited from University of Kent news release.