Bumblebees collect up to 7 times more toxic metals than honeybees

Heavy metal pollution is common around industrial sites, mining regions, cities, and towns, but contaminants can also spread into rural landscapes through the air, sewage sludge, fertilizers, and other agricultural products.

How Bees Pick Up Heavy Metals

As bees gather nectar and pollen, they are also exposed to contaminated soil, dust, and pollen that may contain heavy metals. Even relatively small amounts of these elements can interfere with learning and memory, making it harder for bees to navigate and find food. Previous studies have also linked metal exposure to lower reproductive success, fewer offspring, and disrupted brood development.

Honeybees have long been used as biological indicators of environmental contamination in heavily polluted locations. However, the new study, published in Ecological Entomology, the journal of the Royal Entomological Society, shows that different bee species accumulate toxic metals in very different ways, with bumblebees appearing to be especially vulnerable.

Comparing Bumblebees and Honeybees

Researchers from the University of Cambridge's Department of Zoology collected pollen using pollen traps and measured levels of arsenic, cadmium, chromium, cobalt, lead, and tin in both pollen and adult bees. They compared honeybee and bumblebee colonies located side by side in Cambridgeshire, England, where soil contamination is generally considered low.

Although both species were foraging across the same landscape, the results showed striking differences.

Pollen collected by bumblebees contained between two and seven times more heavy metals than pollen collected by honeybees across most of the metals examined. Bumblebees also accumulated roughly three times higher concentrations of heavy metals in their bodies.

Dr. Sarah Scott, who conducted the research while at the University of Cambridge and is now based at Newcastle University, said: "Most metal levels we found were not high enough to kill bees, but even low levels can still harm bee health and colony success in subtle but important ways, such as affecting their ability to forage and reproduce."

Why Bumblebees Are More Exposed

The researchers say the differences likely result from a combination of bee biology and foraging behavior.

Honeybees typically nest above ground in hollow trees or managed hives, and their colonies usually contain between 30,000 and 60,000 bees. Bumblebees, by comparison, build nests underground in soil or leaf litter, and their colonies are much smaller, usually numbering between 50 and 500 individuals.

The two species also forage differently. Flower selection varies based on nutritional needs, body size, tongue length, and feeding habits. Because some plants absorb more heavy metals than others, those preferences can influence how much contamination bees encounter.

Honeybees gather pollen from many different flower species, which may dilute contaminants across their food supply. Bumblebees collect smaller amounts of pollen from fewer plant species, making their exposure more dependent on whether those particular plants contain elevated metal levels.

Honeybees also travel much farther while foraging, sometimes covering distances of up to 10 km from the colony. Their larger workforce allows them to spread across a wider area and potentially avoid contaminated locations. Bumblebees usually forage within about 1.5 km of their nests, giving them fewer opportunities to avoid local pollution.

Another factor may be their appearance. Bumblebees have much hairier bodies than honeybees, making it easier for dust and airborne particles containing heavy metals to cling to them before being carried back to the nest with pollen.

Hidden Risks Even in Rural Areas

Professor Lynn Dicks from the Department of Zoology at the University of Cambridge, the study's senior author, said: "Even in areas that we usually consider safe or lower risk for heavy metals -- typically rural areas, away from industrial or mining areas -- bees can pick up toxic metals. Bumblebee colonies tend to have fewer workers available to perform tasks, so the loss of individuals can have a big impact on overall colony function."

Despite the findings, the researchers emphasize that people should continue planting flowers to support pollinators.

Dr. Scott added: "Bees play a critical role in both biodiversity and food security, so we'd still encourage people to plant flowers to help them, even if you live in an area more likely to be contaminated. At the end of the day, bees still need food. Even if it carries traces of heavy metals, having some food is better than having no food."

The research was funded by the Royal Society. Professor Dicks is also a Fellow at Selwyn College, University of Cambridge.