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Honeybees sleep less when they are exposed to artificial light at night, which could affect their ability to communicate and pollinate plants.

鈥淛ust like humans, honeybees need sleep,鈥� says at the University of California, San Diego. For example, honeybees that haven鈥檛 slept are less precise at performing the waggle dance 鈥� a sequence of movements that tells other bees where to find nectar-rich flowers.

Honeybees don鈥檛 sleep over a single period like humans, but take naps throughout the day and night instead. Unlike other insects, they are usually protected from light at night due to being cocooned in their hives. However, says Nieh, there are two situations in which bees can be exposed to artificial light at night.

The first is when a young queen flies off with a portion of the colony to look for a new nest site 鈥� a process known as swarming. 鈥淲hen bees are in a swarm, they can spend four to five days outside,鈥� says Nieh.

The second situation is when bees are overheated inside the hive, so they go outside and fan the entrance. This is called bearding.

To study the effect of artificial light on bee sleep, the researchers put dozens of western honeybees (Apis mellifera) into two clear boxes, each with air holes, food and an incubator. One of the boxes was illuminated for five days to simulate bearding near artificial light. The other was kept in constant darkness for the same period, as bees often remain in the hive during winter or poor weather.

The researchers monitored the bees using infrared cameras, and whenever a bee was motionless for 5 minutes, this was recorded as sleep. The team found no difference in sleep time between the two boxes for the first 95 hours. But after this time, bees exposed to constant light started to sleep significantly less.

Nieh says the findings suggest that bees are resilient to a few days of constant light, but experience significant adverse effects after about three days.

This effect on their sleep could affect the ability of honeybees to pollinate plants, says Nieh. 鈥淎bout one in every five bites of food [eaten by humans] is due to insect pollination,鈥� he says. 鈥淣ot all of this is due to honeybees, but they definitely play a huge economic role.鈥� Climate change might result in bees bearding more frequently, increasing their exposure to artificial light, he says.

The findings are particularly relevant to urban beekeepers, says Nieh. 鈥淚t would be good to avoid putting honeybee colonies near roadsides or where there are streetlights,鈥� he says. Next, he plans to study the effect of artificial light on bee species that nest out in the open, such as the dwarf honeybee (Apis florea).