detail of ant
September 18, 2017

‘Lazy’ ants found to be ‘bench players’ in ant colonies

While ants have a reputation for being intensely hard workers, previously published research has actually shown that at any given time, more than one-third of the ants in any given colony spend most of their time doing absolutely nothing – and now scientists think they know why.

In 2015, researchers from the University of Arizona found that approximately 40% of the ants in observed groups were almost totally inactive while their colleagues worked tirelessly to complete tasks essential to the colony’s survival. Further study revealed that these ants were not just being lazy – inactivity was their “specialization,” like how some ants foraged or built nests.

“Interestingly, we found laziness to be a behavior in itself,” Daniel Charbonneau, a grad student in the university’s Entomology and Insect Science department and one of the author of the 2015 paper, said at the time in a statement. At the time, however, the reason for this behavior remained unknown. Now, however, he and his colleagues believe that they’ve solved the mystery.

Writing in a recent edition of the journal PLOS One, Charbonneau, his professor (and co-author of the original study) Anna Dornhaus and Takao Sasaki from the University of Oxford explained that these so-called lazy ants are actually a reserve workforce that step in and pick up the slack if active workers need to be replaced. To borrow a sports analogy, they’re bench players.

“Serving as a replacement workforce is a long-held suspicion about the function of ‘lazy’ ants, but it was just an assumption, and never had been empirically confirmed,” Dornhaus noted last week in a statement. So she and her colleagues conducted experiments to put this notion to the test.

Removed ‘bench players’ are not replaced, researchers found

While observing a colony of ants belonging to the species Temnothorax rugatulus, Charbonneau and his co-authors identified and removed the ants that represented the top 20% of the workforce – those ants deemed to be the most active – to see how the inactive workers would respond.

Within one week, they found that these “bench players” stepped up and took over the roles that had been vacated by the ants that were no missing. These ants increased their levels of activity to match those of the lost workers, and the colony went about business as usual, they explained.

Charbonneau said that the ants being monitored were marked with paint on their head, thorax and abdomen so that they could be tracked in recorded  video footage. Since they studied these ants in the wild, he said that they did not know “how quickly their populations turn over in their natural habitat.” But, he added, “it doesn't take much for a colony to lose a bunch of workers.”

In a separate experiment, Charbonneau and Dornhaus removed the least active 20% of the ants and found that, unlike the hardest workers, these ants were not replaced. In other works, ants that were busy building or foraging were not removed from those tasks to replace lost members of the inactive workforce.

“My speculation is this: Since young workers start out as the most vulnerable members of the colony, it makes sense for them to lay low and be inactive,” said Charbonneau. “And because their ovaries are the most active, they produce eggs, and while they're doing that, they might as well store food. When the colony loses workers, it makes sense to replace them with those ants that are not already busy pursuing other tasks.”

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Image credit: Jen Fogarty/(C) AntWeb.org