New research reveals that bumble bees often prevail in direct confrontations with invasive Argentine ants at feeding sites, but these encounters lead to prolonged aggression that reduces their food collection. This added pressure exacerbates challenges for bumble bee colonies already facing habitat loss, diseases, and pesticides. The study highlights how such interactions could impact these vital pollinators.
Bumble bees battling invasive Argentine ants may emerge victorious in individual fights, but the encounters ultimately drain hive resources through lost foraging time and wasted energy. According to a study published in the Journal of Insect Science, these 'nectar wars' force bees to avoid ant-occupied feeders, limiting their access to food despite their physical advantages.
The research, led by former University of California, Riverside entomology graduate student Michelle Miner and conducted in the lab of UCR professor Erin Wilson Rankin, analyzed over 4,300 individual behaviors from more than 415 bumble bees across six colonies. In a shared foraging arena, bees approached feeders either with or without ants present. Argentine ants, known for biting rather than stinging, dominate resources by overwhelming in large numbers. "They can dominate a food resource just by showing up en masse," Wilson Rankin said.
Bees consistently avoided feeders with ants, and as ant numbers increased, so did the likelihood of bites—though not fatal, these prompted bi-directional aggression. Bees retaliated using their mandibles, sometimes decapitating ants. "We do see the aggression being bi-directional," Wilson Rankin noted. "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." No stinging was observed; instead, bees used mandibles for defense. "Mandibles are like teeth but not only used to chew," Miner explained. "They can flare open to handle flowers or crunch a foe."
Despite winning most one-on-one clashes due to their larger size, bees engaged in repeated aggressive exchanges rather than resuming foraging. "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." This shifts bees into attack mode, halting food gathering. "They're wasting energy, they could be getting harmed, and they're not bringing food back," she added.
Bumble bees face mounting threats from pesticides, habitat shrinkage, and diseases, making ant interactions a potential tipping point. Miner emphasized their pollinator role: "With how important bumble bees are as pollinators, it made sense to try and understand more about what's going on in these tiny nectar wars, because they could have a big impact."
Scientists remain uncertain about colony responses to underperforming foragers. "We don't know if the colony sends out additional foragers when one comes back short," Wilson Rankin said. "That's the next question it's important to answer." The full study is detailed in the Journal of Insect Science (2025; 25(6)), DOI: 10.1093/jisesa/ieaf076.