When larvae need to be fed or pupae need attention, brood-tending bumblebee workers stay awake to take care of them and don’t suffer sleep-deprivation symptoms, according to a study published in Current Biology by Hebrew University of Jerusalem scientists.

“This is the first evidence that animals give up sleep to care for offspring that are not their own,” write co-authors Moshe Nagari, Ariel Gera, Sara Jonsson and Guy Bloch.

“Our findings show that sleep is more plastic and less rigid than is commonly accepted,” said Bloch, a biology professor whose groundbreaking research on circadian cycles focuses on bee behavior.

Bloch and his colleagues in the Department of Ecology, Evolution, and Behavior had earlier shown that bumblebees’ social interactions and division of labor synchronize their internal clocks. The circadian rhythm of “nurse” bees switches off while they are providing around-the-clock newborn care.

In the new study, they discovered that nurse bumblebees forgo sleep even when the brood they’re tending does not need feeding.

“The fact that the nursing bees sleep so little, even when caring for pupae that do not need to be fed, was the most surprising,” Nagari said. “Before this study, we assumed that the main functions of activity around the clock without circadian rhythms in nurse bees is to provide improved feeding to the developing larvae, enabling them to grow rapidly.”

Pheromones produced by the pupae – even when present in an otherwise empty nest – seem to induce the reduction in sleep. And this naturally induced lack of sleep does not affect the worker bees’ health or everyday function as sleep deprivation normally does.

Bloch and his team point out that animals such as birds and fish make do with less sleep during migration and mating seasons.

“If there is no cost for sleep loss, it means that the brood-tending bees have mechanisms allowing them to significantly reduce sleep without a cost to the brain and other tissue,” Bloch said. “This of courses raises the question about what exactly are these mechanisms and what is the basic function of sleep.”