I'll bet you this, from this remote ranch 13,000km from Thailand: there's no buzz filling my favourite Thai mango orchard now.
I don't have to be there to know. By late November, year after year, the swarms of giant honey bees, Apis dorsata, depart the orchards in Mae Hong Son for their new nesting sites.
Every autumn, beginning in mid-September, big groups gather there, having departed old nesting sites. The huddled swarms of bees hang from tree branches -- some as small as grapefruits, composed of just a few hundred bees, but others the size of LeBron James, holding up to 200,000 individuals.
The swarms are awe-inspiring. The bees themselves are lovely, nearly twice the size of familiar European honey bees here in the United States, and coming in colours from creamy yellow to deep orange and black. They bivouac as they rest during long migratory flights -- just as you might make a stop at a 7-Eleven for fuel and a soda, the bees are forage for sugary nectar, refuelling their hungry bodies for the remainder of their trip.
The bees in their hanging bivouacs battle big, voracious hornets and fierce weaver ants. They warn birds, such as chestnut-headed bee-eaters, and humans to stay away, with a mesmerising, shimmering wave which spreads over the entire cluster as individual bees flick their abdomens in rapid succession. If you're smart you pay attention to escalating warning signals. These are the bees that long-time Cornell University apiculturist Roger Morse called "the most dangerous stinging insects on earth".
As a swarm rests and forages, one day a few scout bees will begin dancing. Their performance is a peculiar, prolonged, stuttering variation on "the waggle dance" famously described in the 1940's by Nobel Prize winner Karl von Frisch. Other bees encircle and follow the dancers, and after perhaps two hours of this, the entire group becomes agitated and lifts off, flying swiftly and precisely in the direction indicated by the dancing scouts. They're headed for a new home, or at least another resting spot on their migration to higher altitude for the dry season. There each swarm will build a single, large new comb and start a new nesting cycle. As of late November, all the swarms are gone from the orchard.
How can I be confident of all this, all the way from Wyoming? In an open-access paper published online Nov 1 in the Journal of Insect Science, I recounted my experience with the migrating bees of northwestern Thailand in the three autumns I worked there between 2009 and 2016. It appears the bees gather predictably in the same place and at the same time every single fall.
Why the mango orchard? As the dry season comes, the bees are on a trek of many miles from one nesting site to another, "surfing" the bloom of nectar-giving plants as they seek sweeter pastures. They need a rest stop or two. This orchard is flanked by tall eucalyptus and teak trees whose flowers provide abundant nectar. The orchard hugs the shore of the Pai River, a navigational guide and corridor for the migrants and a source of cooling water as the bees hang in the hot Thailand sun. The shading mango trees have rough-textured branches angled to the bees' preference for forming bivouacs.
Who cares? Well, Thais, and everyone living across the Asian range of the giant bees --from Afghanistan to the Philippines, and southern China to Indonesia -- should care.
Bees are important pollinators of sub-tropical fruit, nut, and vegetable crops, and of wild flowering plants in these lush ecosystems. Giant honey bees nest scores of metres high in the tallest forest trees, in large aggregations of colonies. They make delicious honey, which brings a good price and is highly sought by local people. The honey is harvested by intrepid traditional hunters who say Buddhist prayers before climbing the terrifyingly rickety bamboo ladders to face off with the multiple nests of bees, using smoking dung or straw to drive the bees from their combs, and sharp machetes to cut out the honey combs.
Giant honey bees are threatened. Studies in India and Nepal document drastic declines in numbers of Apis dorsata and its close relative, Apis laboriosa, over the past 30 years. Honey hunters and scientists who have worked in northern Thailand tell me there are far fewer colonies of giant honey bees than in the recent past. Bee scientists have long considered the loss of tall nesting trees and foraging habitat, as well as the over-harvesting of honey and widespread pesticide use, to be the major threats. My research indicates that stopover sites may also be critical to the livelihoods of the bees. If such sites are destroyed, migrating bees that are famished and exhausted may have nowhere to rest and refuel.
It seems likely that stopover sites are getting destroyed everywhere. Remarkably enough, this Thai orchard is the only stopover site that has ever been regularly described by honey bee researchers. I'll bet our Wyoming ranch that such stopover sites were common throughout most of the range of giant honey bees. But sites located along rivers are prime areas for agricultural development and its associated habitat destruction. In Thailand, rice paddies, vegetable fields and fruit orchards have largely replaced native plants in riparian areas.
We have long known the importance of migration and stopover sites for many species of birds. Consider the great efforts in the United States by the National Audubon Society and many others to protect the Platte River in central Nebraska, which provides crucial stopover sites for migrating sandhill cranes. Along the east coast of the US, migrating red knot shorebirds are heavily dependent on a springtime stopover site at Delaware Bay for a sustaining, but endangered, meal of horseshoe crab eggs. In the past two decades in my state of Wyoming, state and university wildlife biologists have learned much about the regional migrations of deer, pronghorn and elk and the habitats that nurture them.
We know much less about the migrations of insects and what sustains them. But looking to monarch butterflies as an example, citizens' initiatives have greatly helped in the elucidation of their migration routes and needs. I urge researchers and private citizens in southern Asia to search for stopover sites throughout the range of the giant honey bee as part of their efforts to conserve them. This may be a perfect opportunity to involve citizens in science. Local scientists and field workers often know when bees are on the move from one nesting site to another. At those times people should search for bivouacking bees, particularly in trees along rivers, between known nesting sites. When they find resting sites, they must encourage their governments to enact policies to protect them. It may be one of the surest ways to keep these spectacular bees surfing their sweet wave, and pollinating plants along the way, well into the future.
WS Robinson is an emeritus instructor at Casper College in Casper, Wyoming, where he taught various biology-related classes. He has worked with and studied bees in many countries worldwide. He took part in research on the bees at the Royal Project in Mae Hong Son in 2009, 2010 and 2016.
