Tropical insect infestation in Dalmatia: "A species not seen for nearly 50 years has returned"

A tropical species of wasp has returned to Dalmacia after nearly five decades, according to local biologist Dr. Toni Koren. The discovery, made in July 2025 near the castle of Kaštela, marks the reappearance of the Oriental hornet, a species previously unseen in the region since the 1970s. The finding has sparked interest among entomologists and environmentalists, who see it as part of a broader trend linked to climate change. The Oriental hornet, known for its striking black-and-gold appearance, was spotted by Koren during his exploration of a cave system near Kaštela. He had initially noticed the insect through a social media post shared by a Slovenian group, prompting him to investigate further. Upon arrival, he quickly identified the specimen and captured it with a net, expressing surprise at the confirmation of its presence. “It was a shock,” he said, noting that the species differs significantly from the native hornet in both coloration and behavior. Koren explained that while the Oriental hornet is not inherently aggressive toward humans, it can become defensive when provoked. It typically bites only when handled roughly, such as when someone sits on it or applies pressure. He warned that individuals allergic to stings should exercise caution, as reactions can develop over time. “It’s always uncertain whether a wasp will sting you,” he said, emphasizing that some people might be bitten multiple times without immediate symptoms, only to later experience an allergic reaction. In addition to the Oriental hornet, other invasive species have already established themselves in Croatia. The Asian tiger mosquito, for instance, has taken root in the country, aided by warmer temperatures and milder winters. According to Koren, these changes in climate have created favorable conditions for new species to thrive. “We can expect more arrivals,” he said, pointing out that certain mosquito species already present in neighboring countries may soon reach Croatian territory. The Asian tiger mosquito poses particular concerns due to its potential to spread diseases such as Zika virus and dengue fever. Koren highlighted that these mosquitoes often breed in small pools of stagnant water, frequently found in cemeteries, flower pots, and other artificial containers. He urged residents to eliminate such breeding sites, especially around homes, to reduce their numbers. “They tend to enter houses during the day and bite people directly,” he noted. Despite the growing presence of exotic species, Koren stressed that most of them are not dangerous to humans or ecosystems. He pointed out that many new arrivals, such as stoneflies, butterflies, and moths, are harmless. Among the notable newcomers is the black swallowtail butterfly, which was first recorded in Croatia in 2025 and has since expanded its range to the Kvarner region. “These species are not harmful,” he said, adding that they represent a natural shift in biodiversity driven by changing climatic patterns. While tropical species may struggle to fully establish themselves in Croatia due to differences in climate, some have already begun to cause issues in neighboring regions. One example is the Asian hornet, which is prevalent in Italy but has yet to be documented in Croatia. This species is particularly concerning because it competes with honeybees for food, potentially disrupting local pollination systems. In Italy, specialized services monitor and control the spread of the Asian hornet, and Koren suggested similar measures could be necessary in Croatia as the situation evolves.