The animal kingdom is known for its bitter rivalries that sometimes erupt into all-out feuds, such as the conflict between bumblebees and Argentine ants. When these two insects meet, it is not uncommon for them to compete to feed on flowers. And the battle that ensues doesn’t end well for either of them.
A new study published in the Journal of Insect Science documents a serious dilemma bumblebees face when Argentine ants compete with them for nectar. Bees tend to avoid flowers already occupied by aggressive ants, which bite to keep them away, but when the two become entangled in a fight, the bees sometimes bite. In most cases, these skirmishes are a lose-lose scenario, leaving the ants dead and the bees wasting energy that could have been spent feeding their colonies.
Learn more: The fragile future of solitary bees
Argentine protective ants
Argentine ants are native to many countries in South America, but have been introduced as an invasive species to several regions of the world, including European countries bordering the Mediterranean Sea, coastal California, South Africa and Japan. Argentine ant colonies are known for their aggressiveness, quickly expanding into new areas and displacing native ant species.
In Southern California, these ants are often found in citrus groves, where they are a considerable nuisance due to a special partnership with other pests. This takes the form of a quid pro quo agreement with insects of the order Hemiptera (or “true insects”), including psyllids, scale insects and aphids.
Argentine ants will protect these other insects from their natural enemies and, in exchange, they will have easy access to honeydew – no, not the fruit, but a sweet liquid secreted by many hemiptera. The ants then collect the honeydew offered to them and return to their nests to feed the colony. They will also lead their hemipteran co-conspirators to new feeding sites, thereby exposing entire citrus groves to the risk of pest invasion.
Bumblebees’ Most Annoying Enemy
Although Argentine ants are friends with other pests, they are not so fond of bumblebees. When ants on a flower receive a visit from a bee, they bite it to keep it away from the nectar.
Naturally, these nectar thieves are bad news for bumblebees, which generally choose to avoid flowers that have Argentine ants on them. However, they are sometimes drawn into a fight when an ant starts biting.
The researchers involved in the new study wanted to see exactly what was happening during this conflict. To do this, they observed more than 4,300 individual behaviors of more than 415 bumblebees.
“Given the importance of bumblebees as pollinators, it made sense to try to better understand what’s happening in these little nectar wars, because they could have a big impact,” author Michelle Miner, a former entomology graduate student at the University of California, Riverside, said in a statement.
The results of the nectar wars
The researchers introduced six separate bumblebee colonies into a feeding arena with feeding sites where there were ants nearby or without ants. Not surprisingly, bees were less likely to attempt to forage at a site with more ants.
Some bees, however, visited sites with ants on occasion. When the ants began to bite, the bees responded not by stinging, but by biting and decapitating them. This morbid outcome led to frequent bee victories in one-on-one fights, but this was not necessarily a victory for entire bee colonies.
The researchers found that bees that fought off ants were five times more likely to continue engaging in aggressive interactions rather than switching to non-aggressive interactions. These combative bees were also eight times more likely to pursue aggressive interactions than to feed.
In other words, bees stuck in attack mode do not bring food back to their colonies. How colonies respond to missing food is not yet known and researchers hope to answer next.
Bumblebees that run into ant antagonists may leave with injuries and without food, potentially leaving colonies starving or losing a limb. It might be better then if they just be the biggest bee and move on to the next flower.
Learn more: Ants can amputate other ants to save them – is this a sign of empathy?
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