Rising temperatures shift mosquito species and disease risk across Europe — UnionPress

A late start to Latvia's mosquito season and expanding mosquito maps in the EU signal climate‑driven changes that could affect public health and ecosystems.

Latvia's mosquito season began later than usual this year, with the first noticeable swarms arriving around 24 June after a dry, quiet June. The delay, entomologists say, reflects the twin climate factors that govern mosquito life cycles: temperature and water availability.

Warmer air speeds up larval development, while standing water provides the breeding sites mosquitoes need to lay eggs. A dry spring can dry out puddles and other temporary pools, postponing the emergence of adult insects even when temperatures are favourable.

Beyond the nuisance of itchy bites, the timing, distribution and species composition of mosquitoes are emerging as a barometer of the climate crisis. Researchers warn that shifts in these patterns could reshape ecosystems and raise the likelihood of mosquito‑borne diseases in regions that have historically been low‑risk.

"Mosquitoes occupy both land and water habitats and serve as a substantial food source for many other animals," explains Jānis Graudiņš, an entomologist at Latvia's scientific institute BIOR. "Their larvae are eaten by fish, amphibians and dragonflies, and they help decompose organic matter in water bodies."

Adult mosquitoes, contrary to popular belief, feed mainly on nectar; only females bite when they need protein for egg production. Those blood‑feeding females become prey for birds, bats and other insectivores, linking them to broader food webs. In addition, some mosquito species contribute to pollination, albeit modestly.

BIOR launched its first national mosquito‑monitoring scheme only in 2023 and has so far identified around 40 species. The programme relies on traps that capture insects, but the data are still too sparse to determine long‑term trends such as population growth, decline or the arrival of new species.

Last year, a single specimen of the invasive Asian mosquito Aedes japonicus was caught. While a lone find does not prove the species has established a breeding population, it demonstrates that pathways exist for non‑native mosquitoes to reach the Baltic region.

Climate models predict that as Europe warms, cold‑adapted mosquito species will retreat northward while southern species expand their range. This biogeographical reshuffling could alter the risk profile for diseases like West Nile virus, which requires a certain temperature threshold to develop inside the insect before it can be transmitted to humans. Latvia's current summer temperatures rarely reach that threshold, but a modest rise could make the virus viable locally.

Neighbouring countries already have more extensive records. Since 2020, the Dutch citizen‑science project Muggenradar, coordinated by Arnold van Vliet at Wageningen University & Research, has collected public reports on mosquito nuisance, sightings and protective measures. Participants occasionally submit captured specimens for laboratory identification.

"Mosquito nuisance is subjective," van Vliet notes. "One mosquito in a bedroom can feel worse than a swarm in a garden, but aggregated observations give a reliable picture of local mosquito activity."

The Dutch data reveal a growing presence of the urban‑adapted Culex pipiens molestus form, which prefers mammalian blood and can thrive in underground water‑filled spaces. This is significant because the related Culex pipiens form primarily feeds on birds and is the main vector for West Nile virus. Hybridisation between the two forms can produce mosquitoes that bite both birds and humans, potentially bridging the virus from avian reservoirs to people.

"If West Nile virus is circulating, the risk rises when mosquitoes stay active through winter," van Vliet warns, highlighting the importance of continuous surveillance.

The European Centre for Disease Prevention and Control (ECDC) reported 304 locally acquired dengue cases and 1 436 West Nile infections across 19 member states in 2024. By June 2025, the invasive Asian tiger mosquito (Aedes albopictus) had been confirmed in 369 EU/EEA regions, up from 114 a decade earlier.

However, the ECDC admits that surveillance intensity varies widely between countries, meaning current maps may underestimate the true distribution of invasive species. "In the past, a country's map turned red the moment it started systematic monitoring," says ECDC medical entomology expert Olivier Briet. "Consistent surveillance is the only way to detect changes early and act before diseases become entrenched."

In northern Europe, the immediate threat remains lower than in the Mediterranean, but the region is not immune. Invasive mosquitoes have been found as far north as Sweden, usually arriving as eggs attached to goods or vehicles. Migratory birds can transport viruses such as West Nile, Usutu and Sindbis, which may encounter receptive native mosquito populations.

For ordinary Europeans, the shift in mosquito dynamics translates into practical concerns. Increased biting seasons can affect outdoor workers, from construction crews to agricultural labourers, who spend long hours exposed to insects. Health‑related absenteeism and the cost of repellents or protective clothing could rise, especially for low‑paid workers who cannot afford premium products.

Public‑health systems may also face added pressure. Outbreaks of West Nile or other arboviruses require diagnostic testing, hospitalisation and, in severe cases, intensive care. Early detection through entomological surveillance can limit the scale of such outbreaks, but it demands investment in monitoring networks, laboratory capacity and public‑information campaigns.

From a climate‑policy perspective, the expanding range of disease‑carrying mosquitoes underscores the broader social costs of insufficient mitigation. While the European Green Deal aims to cut emissions, the health sector must also prepare for climate‑related disease vectors, integrating vector control into urban planning and green‑infrastructure projects.

Health authorities across the EU continue to advise simple preventive measures: eliminate standing water in gardens, install window screens, use insect repellent on exposed skin and report unusual mosquito sightings to national monitoring bodies. Such citizen participation can fill data gaps, especially in regions where official surveillance is limited.

As climate change reshapes the continent's ecology, the humble mosquito is becoming a useful early‑warning system. By tracking its movements, Europe can better anticipate the ripple effects on public health, biodiversity and the everyday lives of its citizens.