Floodwater Mosquito

Aedes vexans

Aedes vexans adult image from iNaturalist Open Data.

Overview

Aedes vexans is a native floodwater mosquito in the UK. It is most likely to become noticeable after summer flooding in river landscapes and wetlands, where adults can emerge in large numbers.

The species matters for West Nile surveillance because APHA reported West Nile virus RNA fragments in pools of Ae. vexans collected in Nottinghamshire in 2025, the first confirmed detection of West Nile virus in a UK mosquito.

UK Relevance

This is not a species that should cause public alarm. The UK risk of West Nile virus is still considered very low, and there is no evidence of locally acquired human disease. Even so, the detection makes Ae. vexans part of the UK's early-warning picture.

Identification

A native mosquito associated with flooded ground rather than indoor or container habitats.
Adults are usually brown and can be difficult to identify reliably without specialist keys.
Habitat context is important: records from summer-flooded river landscapes and wetland margins are especially relevant.

Distribution in the UK

APHA described Ae. vexans as native to the UK and reasonably rare because of its habitat requirements, but capable of reaching high densities in a few locations associated with summer flooded river landscapes. The 2025 West Nile finding came from Nottinghamshire samples collected in 2023.

Diseases

The main public-health relevance of Ae. vexans in the UK is its role in West Nile surveillance. APHA found West Nile virus RNA fragments in mosquito pools from this species, but that does not mean the virus is established or transmitting locally.

Read more on West Nile virus for the broader UK context.

Prevention & Advice

Reduce standing water after floods, use mosquito repellent when outdoors, and report unusual mosquitoes through the citizen science guidance if you find one in an unusual place.

References & Further Reading

Last updated: 2026-04-06

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