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Where Giant Honey Bees Rest Their Wings During Annual Migration

Apis dorsata bivouac

In a new study published in the open-access Journal of Insect Science, a bee researcher describes the discovery of a “stopover” site in Thailand where Apis dorsata honey bee swarms gather to rest during their annual migration between highland and lowland nesting sites. Shown here is a swarm “bivouac” resting on the underside of a mango tree limb at the stopover site. (Image originally published in Robinson 2021, Journal of Insect Science)

By Ed Ricciuti

Ed Ricciuti

Ed Ricciuti

It literally took a lot of sweat and some worrying about a possible snake in the grass, but it paid off for a scientist from Wyoming, whose research beefs up evidence that conservation of migratory insect pollinators hinges as much on the ecological integrity of pit stops during their journey as conditions at either end.

“I sweated and sweated, and was usually drenched in my own sweat, my shorts soaked through, by mid-day, and because the grass and weeds grew long I worried about venomous snakes,” says Will Robinson, Ph.D., emeritus instructor of biology at Casper College, of his field work in Thailand studying Apis dorsata, known by many as the giant honey bee. It’s a key pollinator of southern Asia, not domesticated but still an important source of wild honey. Robinson’s research is described in a paper published in November 2021 in the Journal of Insect Science, part of a special collection on fundamental and applied aspects of honey bee biology, published in collaboration with the American Association of Professional Apiculturists.

Colonies of giant honey bees migrate with the monsoon season, back and forth between highland and lowland nesting sites. Robinson observed that the migrating bees regularly use a mango orchard in northern Thailand at the same time every year as a stopover bivouac to rest and replenish before continuing on their trip. His discovery of the stopover site in 2009 marked the first one ever documented for the species. It remains so, but he believes many others exist.

Robinson’s subsequent treks to the orchard at the bottom of a steep valley along the Pai River after his discovery of the bee rest area demonstrated that bivouacking by A. dorsata bees there was not a one-off event. “Bivouacking bees occupied almost precisely the same geographical area in 2016 as in 2009 and 2010,” Robinson writes in his report. “Timing of the stopovers was also remarkably similar. … In 2010 the first bivouac arrived 22 September, and field work was terminated with 5 bivouacs still at the site on 19 November; in 2016 occupation of the site lasted from 18 September to 18 November.” He called “the strong year-to-year fidelity that migrating bees showed” to the site “the most salient result” of this research.

Bicycling to his research area from the provincial capital of Mae Hong Son, in the Shan Hills on the Myanmar border, Robinson regularly patrolled the site and its surroundings. He found that swarms of bees arrived and departed steadily until the end of November—the start of the dry season, when teak and Eucalyptus, a key food source, stop blooming and start shedding leaves.

bee bivouac chart

In 2016, bee researcher Willard Robinson, Ph.D., recorded the visits of Apis dorsata honey bee swarms to a “stopover” site in Thailand where they paused to rest during their annual migration between highland and lowland nesting sites. A total of 49 swarms arrived to form “bivouacs” at the site between mid-September and mid-November, with a median stay of seven days. (Image originally published in Robinson 2021, Journal of Insect Science)

Colonies typically migrate to take advantage of blooming at different altitudes of the flowering plants that provide their diet of nectar and pollen. In northern Thailand, at least, it appears A. dorsata colonies move to higher elevations to increase colony population and reproduce by swarming with the onset of the dry season, then returning to lower elevations to build another nest, grow, and swarm again in the wet season.

Like many other pollinators, Apis dorsata as a species shows signs of declining, in its case due to overharvest by honey hunters and felling of the tall tropical trees in which they nest. Evidence that stopovers are essential to giant honey bee survival should help conservation of the species, Robinson says.

“My studies may hold great importance for the conservation of this charismatic and economically important pollinator and honey producer. Bird biologists are finding increasing evidence that there is no conservation of imperiled species without understanding their entire life history, including not just where they nest and overwinter but precisely where their migratory travels take them in between. The same would apply to giant honey bees.”

Robinson says that the stopover he discovered deserves permanent protection, while wondering how many other such undiscovered key stopovers have been eliminated by deforestation. A search should be mounted for other sites that exist, he says, particularly along rivers where landmarks likely occur and between well-known nesting sites at seasons when the bees are on the move.

Associated with a provincial agricultural center, the orchard in which Robinson sweated out his days in the field supplies all the elements of prime habitat for the big bees, which are more than a half-inch long. It has teak and Eucalyptus plants that yield food, a river for water, and a deep valley with slopes covered by teak forest that could serve as a landmark for the bee travelers. The mangoes and other trees also shade the area to a degree that the bees prefer.

Apis dorsata honey bees

While observing Apis dorsata honey bee swarms at a “stopover” site in Thailand, researcher Willard Robinson, Ph.D., noted that each swarm’s departure was preceded by one or more bees, often an aged worker bee (at center, shown here) performing a waggle dance that appeared to indicate the departure direction and, possibly, distance. (Image originally published in Robinson 2021, Journal of Insect Science)

As he observed the bees—carefully, because they are a touchy breed—Robinson noticed some tantalizing clues to their behavior associated with migration. He watched bees that appeared to have scouted out the next stop along the way perform a waggle dance in front of others, similar to the figure-eight performance by which honey bees that have returned from foraging signal to others the direction and distance to food sources.

“About 10 bees at a time follow each of the dancers very closely,” he writes. “The dances convey extremely accurately the direction of the upcoming flight; there is some controversy about whether migration dances indicate the distance to be flown. My data suggest, and my feeling is, that they do, at least roughly.”

Dances were performed by five to 20 bees at a time, about a half hour before the flight departed. It appeared that a short dance in time meant a short flight distance. The scouts, he discovered, were older bees, whose yellow markings turn to orange with age.

Robinson photographically tracked bees as they aged. It seems possible, he says, that some bees may live the six months or so needed to remember the route to a migration site and transmit that information to others. The relationship between longevity and migration, he says, merits further study. Beyond that, he urges exploration for other rest stops along migration paths of giant honeybees in general, noting that “there may be a role for citizen science in such searches.”

Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.

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