Has the Asian wasp arrived in your municipality? In six years it has doubled its expansion area | Climate and environment

The Asian wasp or velutina (Vespa velutina nigrithorax), an invasive exotic species native to south-east Asia, continues its unstoppable advance. The distribution area of ​​the insect in Spain has doubled since 2018, going from 41,700 square kilometers to 88,900 (17% of the peninsular surface) as of 31 December 2024, indicate the latest data from the Ministry for Ecological Transition. The province of Barcelona is the one that has experienced the greatest growth in this period (from 266 square kilometers in 2012 to 7,333), although it is distributed across four provinces. Parallel to the advance on the Mediterranean coast, the velutina also spread to the north, especially in La Rioja, Navarra and Asturias, as well as in some parts of Badajoz and Cáceres. Galicia, where the vespa velutina was already well established in 2012, continues to be one of its main strongholds.

Once the bumblebee is established, the problems begin. The main one is the predation of other insects, especially bees, in addition to damage to fruit production. There is also a risk to public health, as their stings can cause severe reactions in allergic people or when occurring multiple times, although this danger is similar to that of other wasps. This year three people died in Galicia from a velutina bite, which is unusual.

The ministry updates the information every six years – as Europe requires for invasive species – based on data sent by the autonomous communities. On the created map, hornet detections are represented by areas (grids) of 10×10 kilometers. However, these data do not reflect the density of velutina existing in each grid, i.e. whether only one nest was found or more than a thousand, as happens, for example, in Vigo, the most affected city in Galicia.

“The criterion we follow is the identification of a nest; if we verify that it is empty, because the queens have already left, that grid is considered colonized”, indicate ministerial sources. In this way the presence of the wasp is not always confirmed in all the municipalities included in these networks, but rather in the immediate vicinity. Vital information to take maximum precautions and report any sightings of specimens or nests, as early diagnosis is essential to control their expansion.

Locating the insect is not easy and this is why its presence is usually underestimated. The primary nests – where the queen establishes the colony – are small, the size of an orange, they are built in any corner and go unnoticed. When they disperse, secondary ones appear in which there can be more than 1,000 workers, in addition to the queens and males.

At this population density, they are much bulkier, but that doesn’t make them any easier to eradicate. They are usually found on leafy trees and at high altitudes (10-12 meters) or in various human structures that are difficult to access. Authorities warn that specialized personnel and safety equipment are needed to remove them.

Objective: early diagnosis

“The objective is to promptly identify and then apply measures to prevent it from becoming established,” explains Mar Leza, professor of the Department of Biology at the University of the Balearic Islands and coordinator of the Velutina Task Force working group, specialized in the invasion and impact of the wasp. According to him there is “a lack of general coordination in Europe at the level of biosecurity measures; if there were more joint work, it would prevent, for example, everyone from making the same mistakes when their presence is discovered”.

In the Balearic Islands, early control is working, although the invasive reappears from time to time in Mallorca. Success is part of the creation of a multidisciplinary working group. “In the islands we are like a laboratory, because there are very defined entrances, they arrive by sea or by air, they cannot come alone; in other places like Galicia they enter through the Cantabrian coast, through Portugal…”, he explains. What is not clear, he adds, is that “if nothing is done it will continue to advance”.

They developed prototypes to automatically detect species and placed traps in port and airport areas and “these biosecurity measures were found to work”. But there are other places in the country where “you can only protect bees or control invasive populations.” In these areas it is proposed to place traps at the entrance to the hives to prevent the hornets from hunting the honey bees, the main dish of their diet.

In Galicia, more than 14,400 nests were removed between January and September this year, in a pilot plan launched in 2024. This made it possible to double the capture of queens compared to 2024: 230,000 in the first nine months, compared to 113,000 last year. Furthermore, in the last two years the number of warnings about their presence has been reduced by almost 30% compared to previous years without this type of trapping, Xunta indicates in a statement. Information interviews with the population were also held. Experts warn that the traps are not selective and native insects fall into them, with a significant impact on biodiversity.

The expansion of velutina in Galicia is, according to Xesús Feas, a veterinarian specializing in this parasite, an example of what happens when the intervention is not carried out in time. The important thing is to have “real planning, involving the administration, emergency services, beekeepers and citizens, not just implementing spring trapping plans, because the problem is getting worse.” He also warns that we need to review strategies, integrate data collected in the field and see what role time plays in the cycles of this invasiveness. “Research is missing,” he summarizes. Reports to citizens are another of the fundamental legs in this fight.

The species was first detected in France in 2004, possibly due to the accidental importation of hibernating queen wasps from China in some horticultural products. In Spain, the first confirmed date occurred in Amaiur (Navarre) in 2010. In the same year it was also located in the Basque Country, in Guipúzcoa. It is currently widely distributed, as well as in Spain, in France, Belgium, Portugal, Italy and Germany. It prefers temperate zones, without extremes of heat and cold, especially in humid regions.

Their annual cycle begins in spring, when fertilized queens that have spent the winter in hibernation awaken and build a primary nest. There they lay their eggs and the first workers are born. Starting in the summer, the colony grows and moves to a secondary, much larger nest located on tall, leafy trees (10-12 metres) or human structures. In autumn the colony produces males and new queens who mate and then seek shelter for the winter, while the rest of the colony dies from the cold. In this way only the surviving queens start the reproductive cycle again the following spring, and there are more and more of them.