The scene repeats every summer in thousands of Catalan homes: the light off, the silence of the night, and suddenly, the sharp, insistent buzzing that grazes our ear. The reaction is almost a Pavlovian reflex: we turn on the light, look for the little invader on the wall, and with a sharp slap of a slipper, we put an end to the annoyance. Until recently, this domestic victory returned us the tranquility of a bite-free sleep. Today, however, this gesture hides a much more disturbing reality: the mosquito is no longer just an annoying neighbor, it has become the vector for diseases that just four days ago we considered exotic.Catalonia has entered a new epidemiological era. The dengue outbreak in Vila-seca in the summer of 2024, with eight autochthonous cases, was the definitive alarm signal: the virus no longer only arrives by plane, but circulates among us through the tiger mosquito ("Aedes albopictus). This invasive species, recognized by its white stripes and its diurnal activity, has joined the common mosquito (Culex pipiens), the one of a lifetime, which is nocturnal and acts as the main transmitter of the Nile virus. As researcher Rachel Lowe, director of the Global Health Resilience group at the Barcelona Supercomputing Center (BSC-CNS), explains, "Barcelona is a global hub with a high risk of emergency or re-emergence of various pathogens." According to Lowe, rising temperatures and altered rainfall patterns create a "perfect cocktail" for the expansion of these vectors.

The climate crisis is causing high temperatures to arrive earlier than the summer months, and therefore, so too are infestations of mosquitoes, cockroaches, bedbugs, and ticks in our country. This year, in addition, the spring has been particularly rainy, favoring the spread of these animals throughout the country, and the outbreak of pests has become more advanced, especially in warmer areas. Some of these insects, such as mosquitoes and ticks, are vectors of transmission of diseases such as dengue, Zika, chikungunya, and West Nile fever, which are becoming more common in Spain each year. These diseases were previously only seen in imported cases from other countries, but now native outbreaks are frequently detected—that is, transmission not associated with travel—and experts predict that they will eventually become endemic in Spain.