12-05-2025
Study finds 65% decline in urban bee population, heat and land use are main culprits
Across the globe, the diversity of insect species and their populations are falling rapidly. A few research studies have gone as far as to estimate insect biomass has nearly halved since the 1970s. Bees are particularly hard-hit, suffering from habitat loss driven by agriculture and urban development, compounded by the growing effects of climate change.
A latest study conducted by a team of scientists from Julius-Maximilians-Universität Würzburg (JMU) in Germany analyzed the combined effects of land use and rising temperatures on insects at 179 sites across Bavaria. Their research, part of the LandKlif project within the Bavarian Climate Research Network (bayklif), was led by Professor Ingolf Steffan-Dewenter, with the findings published in the Proceedings of the Royal Society B: Biological Sciences.
The findings indicated that insects inhabiting different trophic levels react differently to the combination of increased temperatures and extensive land use. While bee populations in forests are able to withstand the heat, those in urban areas saw a staggering 65% decline. Similar to humans, bees are impacted not just by high daytime temperatures but also by warmer-than-average nights.
According to biologist Dr. Cristina Ganuza, from the Department of Animal Ecology and Tropical Biology at JMU, the impact of night-time temperatures on diurnal insects is particularly significant. This is due to the fact that average night-time temperatures are rising faster than daytime temperatures, further stressing insect populations.
Although insects higher up the food chain managed better with the heat, populations faced challenges in open agricultural habitats. "This can have a negative impact on agricultural production because insects that contribute to natural pest control should be similarly affected," said Dr. Sarah Redlich, research fellow at JMU's Department of Animal Ecology and Tropical Biology.
The study also showed that the situation for these insects improved in areas where agricultural land was interspersed with natural habitats. This mixed landscape provides more diverse environments, allowing bees and other insects to thrive by offering both the resources they need and natural corridors for movement.
The research team focused on understanding how climate change and land use were specifically affecting bee populations. Summarizing their findings into three key insights, the scientists observed that warmer daytime temperatures can boost the number and diversity of bees, but only in natural habitats like forests and grasslands. This underscores the critical need to preserve and create interconnected natural areas within agricultural and urban spaces.
However, the story takes a troubling turn when it comes to warmer nights. As part of their second takeaway, the researchers found that higher night temperatures significantly reduce bee richness across all habitat types. This previously unknown impact reveals a new threat to insects, highlighting the urgency for further research to understand the physiological effects behind it.
Finally, the study revealed that climate change and land use don't affect all insects equally. Insects higher and lower in the food chain respond differently, which could disrupt food webs and important ecosystem services like pest control and pollination.
