Ailing beehives may not sniffle and sneeze, but new research shows that they can run fevers.
Honeybees exposed to the potentially deadly chalkbrood fungus raised their nest temperature about half a degree Celsius, report Philip T. Starks, now at the University of California, Berkeley, and his colleagues. When the researchers took away the threat, the temperature dropped, the team reports in the May Naturwissenschaften.
“I believe this is the first documented case of fever in honeybees,” Starks says. That little heat wave could fight disease as it does in a sick person, he speculates. “Often, very different animals converge on the same solution to similar problems,” he says. “Fever in honeybee colonies is another fine example.”
Bees may be cold-blooded, but they don’t have to be cold. They generate heat by rapidly flexing their mighty wing muscles while holding their wings still. That exertion helps keep larvae in the brood comb at a cozy 33º to 36ºC.
Should the nest overheat, workers regurgitate water and fan their wings. The breeze and evaporation cool their home.
Japanese honeybees can heat to kill, according to Masato Ono and his colleagues at Tamagawa University in Tokyo. They found that when a giant hornet with unstingably tough armor barges into a nest, several hundred defenders surround it. They flex their muscles to push up the temperature to as high as 47ºC around the hornet, and, as Starks puts it, “they bake it.” If the ball of insects were to warm one more degree, it would start cooking bees, too.
To check responses to tinier menaces, Starks and Cornell University’s Caroline A. Blackie and Thomas D. Seeley monitored temperatures in experimental hives provided with a sugar-water supplement. Reserving one hive as a control, researchers contaminated three others’ syrup with spores that can cause chalkbrood. Especially at low temperatures, the fungus turns larvae into pale mummies that look like chalk stubs. “You can snap them in half,” Starks says. Before exposed larvae showed symptoms, however, brood-comb temperatures rose significantly in the contaminated hives. Larvae don’t have much muscle, so researchers attribute the fevers to flexing nursemaids.
In one of the exposed hives, several larvae mummified, but the other two hives showed no signs of disease.
The experiment convinced behaviorist Marla Spivak at the University of Minnesota in St. Paul that “the fever was real.” However, she calls for more research to see if it played a role in fighting the fungus.
She certainly embraces the premise that bees can combat diseases. She’s bred so-called hygienic strains of honeybees that respond vigorously to low levels of chalkbrood. “They sacrifice the infected larvae, yanking them out of the brood comb and taking them outside the hive,” she explains.
The notion of bee fever popped up years ago, says Eric H. Erickson Jr. of the Carl Hayden Bee Research Center in Tucson, Ariz. He recalls anecdotes in which bees clustered in warm spots in their nests when attacked by Nosema parasites.
Evolutionary biologist Paul Schmid-Hempel of the Swiss Federal Institute of Technology (ETH) in Zurich says that it’s “quite plausible” that pathogens trigger bee fevers. Sick crickets and lizards tend to do extra basking in the sun. In a twist, bumblebees attacked by fly larvae seek cold spots, seemingly slowing fly growth so the bees live longer.
James F.A. Traniello of Boston University reports that a dampwood termite has especially elaborate responses to disease. One termite coming upon spores in its nest pounds out vibrations that send buddies fleeing the danger zone.
Termites have an active immune system, appropriate for denizens of decay. Exposure to low levels of pathogens increases a termite’s chances of withstanding a later wallop. Even an unexposed termite seems to pick up disease resistance from nestmates that have pumped-up immunity, Traniello says. He speculates that living creatures owe some of their social life to the relentless menace of disease.