We need to talk about mosquitoes

Latvia’s mosquito season started late this year. It was an unusually peaceful, bite-free month of June. But around Midsummer (24 June), they finally arrived. The dry spring delayed them, entomologists explained: mosquitoes need both warmth and water. Drought dries out their breeding sites (puddles or any body of standing water) while temperature determines how fast they grow, how long they stay active, and which species survive. It might be hard to see much value in a massive cloud of mosquitoes ruining your garden party. But if we look a little closer, changes in when, where, and which ones appear can tell us a lot about how the climate crisis is changing our surroundings. So instead of wishing they would all disappear, let's face the music. A matter of ecosystems Annoying as they are, the ecosystem would definitely notice if mosquitoes vanished. “They occupy two zones, land and water, and there are so many of them that they form a very good food source for other animals,” Jānis Graudiņš, an entomologist at Latvia’s scientific institute BIOR, told us. Mosquito larvae are food for fish, amphibians, dragonflies, and other aquatic animals, and they help break down decaying leaves in the water. Adult mosquitoes feed birds and other insect-eaters – whoever is fast enough to catch them. They also pollinate flowers, as they mainly live off nectar, not blood. “Only females bite, and only when they are preparing to lay eggs,” Graudiņš explained. Early days in Latvia They may seem all the same while circling around your head, but under a microscope, every mosquito is unique: “Each has its own pattern, its own scales. Some have entirely striped legs,” Graudiņš told us. Latvia knows surprisingly little about its mosquitoes. The BIOR institute began its first national monitoring only last year, and has recorded roughly 40 species. But it's still early days before we start seeing patterns. For now, Latvia can only know what the traps caught, not whether mosquitoes are declining, multiplying or changing, or whether a newly recorded species is a new arrival or a long-term resident. Last year, one invasive Japanese mosquito was found, the Aedes japonicus. It doesn’t confirm that the species has settled in Latvia, Graudiņš said, but it shows it can get here. As the climate warms, cold-adapted mosquitoes may retreat north, while newcomers arrive from the south. This movement could reshape the risk of mosquito-borne diseases. The West Nile virus, for instance, needs enough warmth to incubate inside a mosquito before it can spread. Latvia's summers don't reach that particular temperature threshold yet, Graudiņš said. But warmer summers could change that. Is that mosquito bothering you? The Netherlands shows us what years of collecting data can do. Since 2020, the citizen-science project Muggenradar has asked people how bothered they are by mosquitoes, how many they've seen and what protection they use. Occasionally, they ask people to catch the insect and post it to the lab. “Mosquito nuisance is subjective,” Arnold van Vliet, Muggenradar's coordinator at the Wageningen University & Research, told us. One mosquito in your bedroom at night might seem worse than a choir in your backyard. “But if you have enough observations, it gives you a good indication of the mosquito situation in your area.” The collected observations prove the risks of warming temperatures to the mosquito realm. The common house mosquito has two lookalike types: pipiens, which mainly feeds on birds and hibernates in winter, and molestus, which prefers mammals and can remain active in warm, often underground spaces. Muggenradar found more molestus in cities, likely because of water-filled crawl spaces below homes. This matters for the West Nile virus, which circulates mainly among birds and is spread by pipiens. But the two types can interbreed, making hybrids that feed on both birds and mammals. That could bridge the virus from birds to humans. “If West Nile virus is circulating, it becomes risky when mosquitoes remain active during winter,” van Vliet said. This turns mosquito counting into public-health surveillance. Enough blind spots In 2024, the European Centre for Disease Prevention and Control (ECDC) recorded 304 locally acquired dengue cases and 1,436 West Nile infections across 19 countries. By June 2025, the Asian tiger mosquito was established in 369 EU/EEA regions, up from 114 a decade earlier. But monitoring varies by country, so the maps may not show the real spread yet, the ECDC admits. “In the past, we have seen that a whole country ‘turned red’ the moment that that country started monitoring actively,” ECDC medical entomology expert Olivier Briet told us. Northern Europe faces less immediate danger than the south, but the risk is not zero: ECDC has tracked invasive mosquitoes as far north as Sweden, usually carried in as eggs. West Nile, Usutu, and Sindbis viruses can travel with migratory birds and meet native mosquitoes already here. The ECDC, therefore, also insists on watching the mosquitoes: “The stronger and more consistent the surveillance, the earlier countries can detect changes and respond before mosquito-borne diseases become established.” What can people do? Start by emptying any standing water in the backyard, then add screens to your house and repellent to your skin, and report any unusual-looking mosquitoes to your country's monitoring body.