Fat worker ants are likely to survive up to five times longer than skinny foragers when food shortages run rampant in their colony. A recent study found that famished forager ants suffer malnutrition faster because they prefer to pack on high protein rather than carbohydrates.  

"The queen and larvae want protein for growth, but the workers want carbohydrates for energy," explained Audrey Dussutour, one of the study researchers from the University of Toulouse, France.

While being a picky eater may be fine when food is plentiful, Dussutour and her colleague Stephen Simpson, from the University of Sydney, Australia, found that foragers die from malnutrition within 21 days of a food shortage because they have less fat than stay-at-home workers, who can survive in the colony for up to 100 days. 

To test the ants' resilience when subject to an unbalanced diet, researchers established 64 well-fed mini colonies, comprised of 200 residents each. They then assigned each colony to one of four diets: a high-carbohydrate/low-protein diet that was perfectly balanced for the ants' nutrition; a poorly balanced diet of low-carbohydrate and high-protein that would produce malnutrition; a dilute well-balanced diet; and a starvation diet. 

"Usually we use foragers to do these studies because they are supposed to be older so they are supposed to die earlier," Dussutour said.

However, the study revealed that foragers could live almost as long as nest workers when fed the optimal diet. In fact, researchers found that one forager studied survived a staggering 409 days while the last worker held out for 436 days. 

Even still, some foragers fed the dilute well-balanced diet survived for 300 days, while those on the high-protein malnutrition diet struggled, only surviving an average of 21 days. Foragers placed on the starvation diet died most quickly.

Overall, their study shows that when the ants' diet took a turn for the worse, foragers were always the first to die, even though they are the sole supplier of nutrition for the colony. 

"We wondered if it was because they had different tasks or if it was because they were different ages," Dussutour said. But "even the foragers that were young died earlier than the inner nest workers that were old."

Having ruled out age as the cause of the foragers' deaths, researchers measured the fat content of foragers' and workers' bodies as they switched between roles. While some colonies have predetermined social roles, others are more flexible. 

The study showed that a worker's body fat content dropped to 15 percent when it became a forager, while those ants that switched from being a forager to a worker increased their body fat by 30 percent. This confirms that the rate of survival in the face of starvation is most affected by the amount of body fat reserves an ant has. 

"The colonies that had consumed more carbohydrates were more fat and we were able to show that [for ants] the fatter you are the better it is for your survival," Dussutour noted. 

However, foragers are at an immediate disadvantage because they have to be skinny. Otherwise, they won't be starving and therefore motivated to go out to forage.

Researchers noted that a similar phenomenon might help explain the recent collapse of honeybee colonies in the U.S.

"Beekeepers in the U.S. use artificial pollen to boost their colonies and it is very high in protein, so we were wondering if the bees were dying more because of a protein problem," Dussutour added. 

However, further research is required. Their study was recently published in the Journal of Experimental Biology.