This summer, people across the UK may be noticing more dead bumblebees on the pavement than usual, and scientists say there is a reason behind the phenomenon.
The pattern results from a combination of naturally short life cycles, elevated temperatures, and long-term changes in land use, according to Senior Lecturer in Zoology Alex Dittrich of Nottingham Trent University, who explains that extreme heat, pesticides, habitat loss, and other environmental pressures can make survival more difficult for these important pollinators.
Bumblebee workers usually only live for four to six weeks. The colony is arranged to allow this turnover; if a worker dies, the other bees in the hive remove the body to prevent the spread of disease. It is therefore not uncommon to find dead bees on sidewalks. Although this rate of death is normal, further environmental stressors can make survival even more difficult.
A Summer of Record Heat
June recently saw the warmest temperatures ever recorded in England, while the UK as a whole experienced its second-highest June temperatures on record. High temperatures affect bumblebees by interfering with their development, reproduction, and ability to fly.
These temperatures can also push colonies beyond the limits of their natural cooling mechanisms; although bees keep the temperature inside the hive down by waving their wings, this method is only effective up to certain temperatures, and prolonged heat exposure can alter development and threaten long-term population stability.
Higher temperatures also interfere with the timing of biological events. Climate change can also contribute to phenological mismatch, in which species that depend on one another become out of sync with seasonal changes. For instance, bees might emerge from hibernation before flowers are available, or flowers may bloom and then die off before the bees are active. In these situations, the bees are left without access to nectar at crucial times.
Pesticides Compound the Problem
Chemical exposure also affects bumblebee populations. Although the EU and UK have banned the most harmful neonicotinoids, other insecticides like organophosphates, synthetic pyrethroids, and phenylpyrazoles are still widely used. These chemicals can paralyze or kill bees and also interfere with their ability to navigate. Herbicides can also reduce the availability of important food sources, such as dandelions, which are a major source of nectar at the beginning of the season.
Habitat loss also makes these problems worse. Housing development, intensive agriculture, and road construction have reduced the amount of natural land available for bees to nest and find food. The loss of these habitats reduces the ability of bee populations to cope with extra stress caused by heat and chemical exposure, worsening the impact of their naturally brief lifespans.
Why It Matters Beyond the Garden
The number of European wild bee species considered at risk of extinction has increased from 77 in 2014 to at least 172 now, about 10% of the total species assessed. Bees pollinate an estimated 75% of global crops and play a significant role in pollinating nearly 90% of flowering plants.
Dittrich suggests leaving the herbicide out when dealing with dandelions, letting parts of the lawn grow uncut, planting native species, and exploring non-chemical pest-control options first, using chemical treatments sparingly. For a bee struggling on hot pavement, a mixture of two parts sugar to one part water can help revive it. If it is safe to do so, people can also move the bee to a shady spot or flower.
While these measures will not eliminate the wider pressures affecting bumblebees, they can reduce some of the stressors that make it harder for them to survive. As temperatures rise and habitats keep changing, it will become more important to ensure that bees have reliable sources of food and shelter.
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.