Latvia recorded its first noticeable mosquito swarms around 24 June this year, a month later than usual. The delay, observed by entomologists at the Latvian institute BIOR, is being linked to a dry spring that limited standing water despite temperatures that would normally accelerate larval development.

Temperature, water and mosquito timing

Researchers explain that higher temperatures speed up the growth of mosquito larvae, while standing water provides the breeding sites they need. When a spring is dry, the emergence of adult mosquitoes can be postponed even if the weather is warm enough for development.

Monitoring efforts and species recorded

BIOR launched a national mosquito‑monitoring programme in 2023. Traps set across the country have so far identified roughly 40 mosquito species. The data set is still too limited for robust long‑term trend analysis, but it has already highlighted the occasional arrival of invasive species. In 2023 a single Asian mosquito, Aedes japonicus, was captured; while this lone specimen does not prove an established population, it confirms that entry pathways exist.

Climate change and the northward shift of mosquitoes

Entomologists view mosquito phenology as an indicator of climate change. Projections suggest that cold‑adapted species will move north as Europe warms, while southern species expand further into the continent. A modest rise in summer temperatures could bring Latvia’s climate above the threshold required for West Nile virus to develop inside mosquitoes, creating conditions for local transmission that have not been met historically.

Dutch citizen science adds context

The Dutch citizen‑science project Muggenradar, coordinated from Wageningen University & Research, has been gathering mosquito reports since 2020. Participants sometimes submit captured insects for expert identification. Their data show an increase in the urban‑adapted form Culex pipiens molestus, which prefers feeding on mammals and can thrive in underground water‑filled habitats. The related Culex pipiens form mainly feeds on birds and is the principal West Nile virus vector. Hybrid offspring of the two forms are capable of biting both birds and humans, potentially linking the virus to people if mosquitoes remain active through winter.

European disease trends and surveillance gaps

The European Centre for Disease Prevention and Control reported 304 locally acquired dengue cases and 1 436 West Nile infections across 19 member states in 2024. By June 2025, Aedes albopictus had been confirmed in 369 EU/EEA regions, up from 114 regions a decade earlier. The agency notes that surveillance intensity varies between countries, which may lead to underestimation of invasive species distribution. Medical entomology expert Olivier Briet stresses that systematic monitoring triggers immediate risk alerts on national maps and is essential for early detection and prevention of disease establishment.

Implications for public health and the economy

Invasive mosquito species have been found as far north as Sweden, often 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. A longer biting season could affect outdoor workers, raising absenteeism and costs for repellents or protective gear. Public‑health systems might face added strain from outbreaks that require testing, hospitalisation and intensive care.

Early detection and public advice

Early detection through entomological surveillance can limit outbreak size, but it requires investment in monitoring, laboratory capacity and public information. EU health authorities advise eliminating standing water, installing window screens, using repellents and reporting unusual mosquito sightings. Citizen reports can help fill data gaps where official monitoring is limited.