The Asian hornet is harmful to native biodiversity. Therefore, we would prefer not to find this wasp in our nature, and we are investigating how we can best fight it. The province of Noord-Brabant has also joined this research in detecting and destroying the nests as effectively as possible to prevent further spread of this wasp species.
A nest of the Asian hornet can produce up to 150 new queens in the fall, which can establish new nests next year. It is therefore necessary to find and destroy the nest with queen and all. There are different methods for this. This week, a nest was successfully tracked for the first time in the Netherlands and Belgium using a transmitter and telemetry. This nest has – like the other nests found – been eradicated pesticide-free by vacuuming the hornets with a battery vacuum cleaner. The nests were then frozen to kill the remaining hornets, pupae and larvae.
The queen of the Asian hornet is fertilized in the fall and starts her own colony after the winter. She makes a nest the size of a ping pong ball in a warm place where she lays eggs. These eggs turn into larvae, which the queen feeds on self-caught insects, which are rich in protein. After pupation, these become the first workers who then help gather food: proteins for the new larvae and sugar for the queen and the other workers. This allows the nest to grow exponentially. When the nest becomes too small, the workers make another secondary nest. This nest is often within fifty meters of the first – or primary – nest. The queen moves, and the larvae left behind are fed by the workers, who later also move with them. A location high up in a tree is often chosen for the secondary nest, with the new nest growing to the size of a small bouncy ball in late summer. In this nest, new queens are born in the fall, which fly to mate and find a place to hibernate. They start a new nest the following year.
With a transmitter of 0.15 grams
In Craubeek near Voerendaal (Limburg), a nest of Asian hornbills was found for the first time in the Netherlands and Belgium using telemetry, i.e. with a transmitter. A report was received via Waarneming.nl that several Asian Hornbills were foraging on honeydew. Honeydew is a sweet substance secreted by aphids. In addition, hornets caught all kinds of insects here, which were also attracted to the sweet honeydew. Due to the presence of honeydew, the more common wick pot method was unsuitable. Therefore, a 0.15-gram transmitter was strapped to the body of an Asian hornet, which itself weighed 0.39 grams. Such a transmitter emits a high-frequency signal that can be received with an antenna. An hour passed between the time of capture and the release of the animal. Forty minutes later, the secondary nest was located in an ash tree at a height of 18 meters, 520 meters from the capture site.
Successful implementation of the wick pot method
In Obbicht (Limburg) a nest was found using the wick pot method. A beekeeper reported Asian hornets via Waarneming.nl. The Asian hornets were here hunting around hives for honeybees. They also foraged on the recently shed honey cakes and wax seals that had been placed there. The beekeeper had already placed two wicker pots. The wick pots make it easier to catch, track and measure the flight time of Asian goshawks using the so-called wick pot method. This method is already widely used in Flanders. A wick pot is a pot of bait that attracts gophers. For example, a jam jar, with a small hole in the lid, from which a wick made of an old dishcloth sticks out. A mixture of blond beer, sweet white wine and sugar in a ratio of 1:1:1 works as a cheap lure. Seven Asian hornbills were marked on the three wicker pots in Obbicht with an individual color code, which was applied with a felt-tip pen. Using time measurements and direction finding, the secondary nest was found two hours later. It was 365 meters away in a tree next to a street, which made it quite easy to find. The residents had not yet seen the nest, although it was hanging in the tree five meters from their terrace.
Through public announcements
In the fight against the Asian hornet, cooperation with civilians is essential to locate the nests, as is also evident from the above examples. Two other findings last week were made by public reports. In Nuenen, a football-sized secondary nest in an acacia was reported via Waarneming.nl. In Geldrop, a resident reported a primary nest in the cavity wall of a brick shed. From there, the secondary nest was found, which was 29 meters away in the top of an acacia tree at a height of 17 meters.
It is important for the control of the Asian hornet that as many people as possible report sightings of this species and help look for nests. With this help, expansion and compaction of this invasive exotic can be limited, which also reduces nuisance.
The many reports show that the Asian hornet is often confused with the native, much more common European hornet, which has a brown head and thorax. The Asian hornet is smaller and has a black body with orange stripes and black legs with yellow tips. This webinar explains, among other things, the difference between the two types.
Sightings can be reported with a photo via Waarneming.nl. It is not necessary to create an account for this. Remember, not every hornet is an Asian hornet, and there are other insects of that size. Therefore, always compare whether your photo matches the photos of Asian hornets. Placing several wicker pots helps to find the nest quickly and efficiently. We would like to thank everyone who reported and also the people who helped find and fight these nests.
Text: René Janssen, Bionet Nature Research; Daan Drukker, EIS Science Center Insects; Rob Voesten, NaturallyRob; Dominique Soete, Vespawatch Flanders
Photos: René Janssen (lead photo: Asian hornet on dromedary aphid mildew); Dominique Sweet