Apis cerana swarms abscond to battle and elude hornets (Vespa spp.) in northern Thailand
Willard S Robinson
In September-October, 2009, many Apis cerana swarms appeared in a mango orchard along the Pai River. Swarms were under attack by the hornets Vespa velutina and Vespa tropica. Bees employed previously documented defensive behaviours such as protean flight, “shaking” and “heat balling.” Also, swarms formed downward aerial extensions (“tails”), and extensions along their substrates (“arms”). They performed short, saltatory flights which effectively shed hornets. Relieved of their predators, they took longer flights out of the study area. Flights were either: 1. short (0-50 m), mostly hornet-provoked, without preceding dances; 2. somewhat longer (0-146 m), mostly hornet-provoked, preceded by short waggle dances; or 3. long, largely unprovoked, preceded by long waggle dances. The next year only one swarm appeared from mid-August to mid-November. Hornets were absent despite the presence of attractive Apis dorsata bivouacs. These observations supported the hypothesis that swarms abscond to elude hornets in years when hornets are abundant. An alternative hypothesis, that swarms in 2009 were engaged in obligate, annual seasonal migrations, was discarded.