Buzzing threat: How rising carbon dioxide levels endanger larger bees

Kit Prendergast


Pollinators — including bees, flies, wasps, moths, butterflies, and nectar-loving birds — are a cornerstone of our natural environment. By helping plants reproduce, they keep ecosystems healthy and secure vital food crops. Yet climate change threatens the survival of these hard-working animals. While previous research focused on how temperature spikes affect bees, our new study reveals that rising carbon dioxide (CO₂) levels also put pollinators like bees and hoverflies at risk, with larger bees being the most vulnerable. We found that populations of big bees — including Bombus asiaticus and Xylocopa pubescens — were smaller and less genetically diverse in areas with high CO₂. Conversely, small-bodied pollinators might actually thrive in higher-CO₂ environments.

Globally, we face a pollinator crisis driven by habitat degradation, invasive species, and broad-spectrum pesticides. However, human-made CO₂ emissions are another key driver. Elevated CO₂ reduces the protein content in flower pollen and alters nectar chemistry, such as lowering its sugar content, which impairs how pollinators develop and survive. Other research suggests higher CO₂ concentrations disrupt internal body functions, accelerating how quickly insects break down fats.

Our study examined how bees and hoverflies coped with varying CO₂ levels across 25 sites. This is the first time researchers have investigated how natural variations in CO₂ affect pollinators. While conducted in Pakistan, it directly applies to global pollinator networks. Crucially, we controlled for other environmental factors like altitude, temperature, humidity, and rainfall. Our results confirmed that smaller pollinators fared better in higher-CO₂ environments, whereas larger-bodied pollinators were significantly less abundant. We identified Xylocopa and Amegilla bees, two genera found in Australia, as particularly vulnerable. Meanwhile, smaller genera like Ceratina and Lasioglossum did well.

These findings are deeply concerning. Existing evidence shows large-bodied bees are already vulnerable to climate change because they retain more heat, struggle in dry conditions, and have higher metabolic demands. Yet, large bees are our most effective pollinators. They carry more pollen and fly longer distances, transporting genes to new places. Furthermore, many flowers have evolved to match specific pollinator body sizes. For instance, Melastoma flowers are most effectively pollinated by large Xylocopa bees, which use vibrations to release pollen.

To help larger pollinators thrive in a warming world, we must adopt four practical strategies. First, we must protect their habitat by preventing further land clearing. Second, we must ensure pollinators have access to wildlife corridors so they can migrate to areas naturally lower in CO₂, such as dense forests. Third, planting more bee-friendly trees like Eucalyptus, Corymbia, and Banksia will provide essential food resources. Finally, we must maintain populations of larger-bodied bees by reducing competing threats, such as introduced honey bees, to preserve the genetic diversity they need to adapt to rising emissions. To protect our pollinators in a rapidly changing climate, we must act now by preserving habitats and curbing global greenhouse gases.