What happens when ants get lonely? They're unable to digest their food properly and walk themselves to an early death, a study has found.
The findings may provide an insight into the negative impact of isolation on a range of social animals, even humans, say scientists.
The study tracked the behaviour of a species of carpenter ant Camponotus fellah.
Lab colonies of worker ants were studied under four scenarios -- single ants, groups of two, ten, and single workers with three to four medium-sized larvae.
The isolated ants lived just six days, whereas group-living ants lived up to 66 days, the scientists report in journal Behavioural Ecology and Sociobiology .
The scientists say their results show that ants simply don't know how to behave when alone.
"Isolated ants exhibited a much higher activity after social isolation, continuously walking without any rest," says study co-author Dr Laurent Keller, an entomologist from the University of Lausanne.
This behaviour is a recipe for trouble as the ants don't get enough energy to back it up, explains study co-author Dr Koto Akiko of the University of Tokyo.
"Because of this hyperactivity, isolated ants faced an increased energy demand", says Akiko.
"Isolated ants ingest as much food as their grouped nest mates, but the food is not processed fully by the digestive tract", he adds.
Under normal conditions, carpenter ants go out to the field and collect food on a specialised internal structure called crop. Food stored here is not consumed immediately by the ant, but rather taken to the nest for sharing and for their own consumption.
"[Isolated ants] retained food in the crop instead of digesting it which resulted in an imbalance of energy income and expenditure", says Keller.
The scientists say the findings indicate that food intake alone is not enough, suggesting that social interactions are a key aspect for the ant's proper digestive functions, so that food can go beyond the crop and into their stomach.
But further research is needed to understand how the social environment affects food digestion, says Keller.
One hypothesis proposed by Laurent's team suggest that sharing of regurgitated food, a process called trophallaxis, may be a way for morsels of food to become more digestible.
Alternatively, it may be that social interaction affects some neural pathways that promote gastrointestinal activity, notes Keller.
But Dr Ken Cheng, a behavioural biologist at Macquarie University has another explanation in mind, involving gut microbes.
"It would not surprise me if gut bacteria, which would be passed around with the exchange of food, played a role as well in the adverse effects of isolation," says Cheng, who was not involved in the research.
While the current research is focused on a humble little ant, the findings reported offer valuable insights into how social interaction affect health, and may open the way for future research on other species, says Akiko.
"Evidence is accumulating that social isolation increases the risk of many health problems, including mental disorders like depression and also physiological disorders like cardiovascular or cerebrovascular disease," he says.
"Living alone or feeling lonely also increases the chance of disability or early death in various animals, including humans."
Future research on this front will focus on how gene expression profiles differ between isolated and grouped ants, say the scientists.
They say such an approach may provide insights into the molecular mechanisms at play when ants get lonely and may identify the genes involved in the observed behavioural changes.