Bumble Bees and Ants: A Costly Conflict for Pollinators

Bumble bees may win individual battles against invasive Argentine ants, but a recent study reveals these victories come at a significant cost to the hive’s overall efficiency. While capable of defending themselves, the time spent fighting ants reduces the amount of nectar foragers can collect, potentially impacting colony health.

The Nectar Wars: A Stressor for Bumble Bees

Bumble bees are already facing numerous threats, including habitat loss, disease, and pesticide exposure. Researchers are increasingly focused on understanding how other factors, such as competition with invasive species, contribute to their decline. Michelle Miner, a former UC Riverside entomology graduate student, initiated research to determine if aggressive ants were adding to the pressures on these vital pollinators. “With how important bumble bees are as pollinators, it made sense to attempt and understand more about what’s going on in these tiny nectar wars, because they could have a big impact,” Miner said.

Lab Study Reveals Bee Behavior

The study, published in the Journal of Insect Science, analyzed over 4,300 individual behaviors from more than 415 bumble bees. Experiments conducted in the lab of UCR professor Erin Wilson Rankin involved six bumble bee colonies foraging in an arena with feeders, some near ants and others ant-free. This allowed researchers to observe bee choices and interactions.

Argentine Ants: A Formidable Foe

Argentine ants, likewise known as sugar ants, don’t sting but can bite and overwhelm insects with their sheer numbers. “They can dominate a food resource just by showing up en masse,” explained Wilson Rankin. Bees generally avoid feeders heavily populated by ants, and the likelihood of being bitten increases with ant density.

Aggression Goes Both Ways

While bees attempt to avoid ants when possible, conflicts do occur. The research showed aggression is mutual. “Sometimes you’ll see ant heads on the bee legs because they were feeding and in response to an attack, the bee bit the ant and decapitated it,” Wilson Rankin noted. Although bumble bees can sting, Miner did not observe stinging during the trials. instead, bees primarily used their mandibles – jaw-like structures – to fight.

Winning Battles, Losing the War?

Bumble bees are typically larger than Argentine ants and often prevail in one-on-one encounters. However, the study found that prolonged aggressive interactions with ants significantly slowed down the bees’ foraging process. “The ant presence induced prolonged aggressive exchanges,” Wilson Rankin said. “Even though that one bee might benefit from being aggressive in the short term, it may not be beneficial for the colony overall.”

Energy Costs and Future Research

When bees engage in defensive behavior, they expend energy and reduce the amount of nectar they collect. “They’re wasting energy, they could be getting harmed, and they’re not bringing food back,” Wilson Rankin said. Researchers are now investigating how colonies respond when foragers return with reduced nectar loads, specifically whether they deploy additional foragers to compensate. “We don’t know if the colony sends out additional foragers when one comes back short. That’s the next question that’s important to answer,” Wilson Rankin added.

Key Takeaways

• Bumble bees can successfully defend themselves against Argentine ants in individual confrontations.
• These battles come at a cost, reducing foraging efficiency and potentially impacting colony resources.
• Prolonged aggression with ants delays nectar collection, hindering overall hive productivity.
• Further research is needed to understand how colonies respond to reduced nectar intake due to ant interference.

Reference: Miner, M. C., & Wilson Rankin, E. E. (2025). Bees modulate behavior during nectar foraging in response to direct ant aggression (Hymenoptera: Apidae and Formicidae). Journal of Insect Science, 15(1). https://doi.org/10.1093/jisesa/ieaf076