Sarah is a member of Okehampton branch of Devon Beekeepers and, in 2018, was inspired to visit Jersey, along with other Devon members, to help with the tracking of Asian hornets and nest location. The experience she gained prompted her to research the available literature and write ‘The Asian Hornet Handbook’. This book is the most comprehensive guide we have in the UK on the life cycle, biology and protection strategy for the Asian hornet if/when it arrives in this country.
The life cycle of the Asian hornet is different to that of the European hornet and needs to be understood in some detail in order to control infestation in the UK. Sarah admitted there were some aspects of the life cycle that we have yet to work out, such as how the insect will behave in our cold, wet climate.
Studies so far suggest the mated queen hornet will emerge from hibernation when the average temperature reaches 13°C, which is likely to be sometime in March in the South West. She will feed on sugary materials to boost her reserves, so is likely to be spotted feeding on Camellia nectar or tree sap. During this feeding period ‘foundress’ queens are able to migrate tens of kilometres before searching for a suitable primary nest site and start the building process.
The primary nest
The primary nest is made of plant material pulped with saliva and water, then shaped into the structure by the mouthparts in a similar way to wasps and European hornets. The nest starts with a stalk or petiole attached to a convenient structure, preferably in a dry and sheltered area. Out houses and sheds are ideal. The cells face down with the bottom end open and the entrance is at the bottom of the structure. The foundress queen builds the nest alone until the first cohort of workers emerge and take over. At this stage the development time from egg to adult takes about 50 days.
The larvae are fed balls of mashed up insect meat and sugary material. They will also regurgitate sugary saliva when requested by the workers. This material is the preferred food of the queen and workers.
As the primary nest grows the development time reduces to around 29 days due to better thermoregulation. If the primary nest site is deemed adequate the nest will be expanded continuously throughout the year but in about 70% of cases the colony will relocate to a secondary nest site within a few meters of the primary site.
The secondary nest
The same fibrous papier mâché material is used to construct the new nest. The entrance is at the side and the walls are built with many bubbles or pockets which help improve thermal insulation. The nest continues to increase in size and may reach 50cm or more, although the nests found so far in the UK have been around 20-25cm.
Sarah pointed out that secondary nests can be anywhere from the tops of tall trees, roof spaces or bramble patches near the ground.
Drones and gynes
By September the queen switches to laying drone eggs, then the female eggs are laid that will become the new queens (gynes). Both types of hornet will spend a few weeks in the nest feeding before flying off. In France, this is usually complete by the end of November. Only the fertilised females survive to hibernate over winter.
Sarah showed an interesting series of pie-charts with the proportions of insect prey captured by hornets in different environments, summarised below. This acts as a warning to anyone keeping bees in urban areas!
Asian hornets ‘hawk’ near bee hives and prey may be caught on the wing or grabbed when it lands on a surface. The hornets then fly to a nearby branch and proceed to dismember the insect, taking only the thorax back to the nest, as it contains the major flight muscles used for feeding the larvae.
The disruption to the bee colony is therefore two-fold: direct predation, and predation pressure which makes the forager bees reluctant to leave the nest, leading to reduced winter stores and high stress levels within the colony.
Sarah went on to describe the various methods of tracking Asian hornets back to the nest site. For beekeepers with only basic equipment the Jersey method has proved effective. This consists of marking workers at feeding sites, spotting the direction they take back to the nest, and timing their return to the bait. By moving the bait station closer to the nest and using further bait stations from different angles, the flight paths noted can be plotted to give a reasonable indication of the nest location. Then you have to find the nest!
Asian hornets do not generally fly more than 700m from the secondary nest, but there could be more than one nest in the area.
Various other methods to help with tracking were described at the end of the talk and also during the discussion. In Asia they tie a small feather to the hornet which makes it easier to follow back to the nest. Unmanned aerial vehicles (UAVs) have been combined with infrared detectors with limited success (nests are well hidden in foliage and well insulated). Harmonic radar has been tried and will work in open spaces but radio telemetry using tagged hornets and a directional antenna/receiver has good potential at the moment. However, tags cost over £100 each, but can be re-used if recovered from the nest.
The talk was attended by over 70 members.
* All images Courtesy The Animal and Plant Health Agency (APHA), Crown Copyright