Gay Marris, PhD, National Bee Unit (NBU)
We begin a formal risk assessment of this looming threat
THE ASIAN hornet, Vespa velutina, is an aggressive predator of honey bees and other beneficial insects. Physically, it is superficially similar to the native European hornet, V crabro, but despite its fearsome reputation V velutina is slightly smaller (2.5–3 cm long). It has a dark ‘velvety’ thorax, from which the subspecies nigrithorax derives its name. Its clearest distinguishing features are that, while V crabro has a comparatively yellow abdomen, in V velutina only the third segment is yellow and it also has yellow legs (see Figures 1 and 2). The lifecycle of the Asian hornet has been described in previous articles (see Bee Craft, September 2007, page 11), but can be summarised as follows (Figure 3): mated queens emerge in early spring and form embryo nests. Larger nests are established rapidly and worker hornets attend to the needs of the growing
colony. Workers are extremely active and predate a variety of insects to obtain the protein-rich diet that the developing hornet brood requires. Prey is often caught on the wing, but hornets also enter honey bee hives to raid severely depleted colonies. Mature hornet nests, which can be huge (Figure 4) and comprise several thousand individuals, are seen from May
onwards. Sexual stages emerge from July until November and one colony may produce hundreds or even thousands of mated queens. As the colony dies, these foundresses seek out suitable sites in which to overwinter. They emerge in early spring, to begin the cycle again. A key feature of the Asian hornet’s biology is that a single, mated queen can found an entire new colony.
The Asian hornet has recently extended its native geographical range from Asia (Figure 5) to mainland Europe, following accidental