Thirsty work Albert de Wilde/Buiten-beeld/Minden Pictures/Getty

Turn the air conditioner on, it’s a scorcher out there. When honeybee hives get too hot, thirsty bees beg their specialised, water-foraging sisters for more liquid, which ends up cooling the colony.

Honeybees have a few strategies for chilling out: some fan the nest, others leave the hive to increase air flow, and a few zip off looking for ponds or puddles. These “water collector” bees fill their bellies with water, fly back home, then regurgitate the liquid. Other bees slurp it up and spit it out around the hive, allowing the colony to cool as the water evaporates.

It was suspected that a steady supply of water is important during extreme heat, says Thomas Seeley at Cornell University in Ithaca, New York. To confirm that, Seeley and his colleagues exposed two hives — each containing about 3000 honeybees — to heat lamps in the lab.


Aquatic quests

When the bees didn’t have access to water, the colonies shot up to about 43°C, a hazardously high temperature: above 40°C, bee larvae can dehydrate and die. When the researchers restored water access, the hives cooled below the lethal threshold.

“[Water] is not just icing on the cake, it’s critical for their cooling,” says Seeley. “Without that, they cannot really control the temperature in the nest on hot days.”

But the researchers weren’t sure how the water collectors knew when more liquid was needed. To find out, they turned up the heat and watched how individual bees responded.

Once the hive ran out of water, the bees that stay home and dole out provisions begged for more by touching their tongues to the mouths of the water collectors, entreating them to spew up more liquid. These solicitations were almost non-existent under cooler conditions.

“They’ve given up their water and they’re still being begged, almost pestered,” Seeley says. “That motivates the water collectors to zoom right out and get more.”

Living storage tanks

The foraging bees largely ceased their excursions once their sisters stopped pleading for more water — but not before they stockpiled some water their hive-mates didn’t spread around, Seeley says.

After a day enduring hot and dry conditions, several dozen bees — both water collectors and others — transformed themselves into living storage tanks, bulging with water stowed in an expandable region of their gut. The bees also stashed some water in honeycomb cells, but, because water can easily evaporate from the comb, “water-bottle bees” may be a more efficient storage method, says Seeley.

Researchers have long focused on how honeybees gather pollen and nectar, while spending relatively little time investigating water collection, says Susan Nicolson at the University of Pretoria in South Africa.

“We just don’t know much about how bees handle water,” she says. “It’s been a bit of a gap.”

The exciting thing about this study is that it clarifies how individual bees are stimulated to respond to a colony-wide need, says James Nieh at the University of California San Diego. “It provides new insight into this mechanism that we’ve long suspected, but now we have more concrete details of how it works,” he says.

Journal reference: Journal of Experimental Biology, DOI: 10.1242/jeb.139824