Guidance

Distinguishing Aedes albopictus, the Asian Tiger mosquito, from native British mosquitoes

Updated 10 August 2017

Public Health England has received a number of mosquito specimens collected in 2016 and reported as possible Asian Tiger mosquitoes (Aedes albopictus), but which do not belong to that species of mosquito.

1. Mosquito species in the British Isles

The UK has 34 native mosquito species, many of which bite and can be a nuisance. There are 2 native species of mosquito that appear morphologically similar to Aedes albopictus.

Recent submissions to the PHE mosquito reporting system have included 2 native species: Culiseta annulata and Aedes geniculatus. Both species are found in urban areas.

2. Culiseta annulata

Culiseta annulata is a widespread and common mosquito of the British Isles, and is also one of the most common mosquitoes in Ireland.

This mosquito breeds in a wide variety of different sites in natural and artificial waters. These can be in sunlit areas or deeply shaded. The water in which the eggs, larvae and pupae are to be found can be fresh or brackish, clean or polluted and may include

• ponds
• ditches
• marshes
• garden water butts
• cisterns

The adult female Culiseta annulata feed both indoors and outdoors on a wide variety of vertebrate hosts including humans. Unlike most British mosquitoes, the aquatic stages, the males and the females are present throughout the year. All stages are able to overwinter.

When there are reports of mosquito biting in late autumn or early spring they can almost always be attributed to Culiseta annulata.

3. Aedes geniculatus

Aedes geniculatus is a striking black and white mosquito with tips to the femora giving an impression of white ‘knees’. It also has a white pattern on the thorax and white patches on the abdominal segments that do not meet in the middle.

The aquatic stages are found in water-filled tree holes, especially in beech. Eggs are laid on the side of cavities and await submergence after rainfall. Adult emergence begins in May and there are 2 generations per year with the last adults occurring in September.

Females of this species bite people readily.

4. Reasons for confusion over identification

The most likely reasons why many people confuse these 2 mosquito species for the Asian Tiger mosquito are:

• Cs. annulata is large and has very distinctive and boldly striped legs similar to Ae. albopictus
• Ae. geniculatus has very white scales on a black body similar to Ae. albopictus

There are 3 important differences between Cs. annulata and Ae. albopictus:

1. although both species have legs that have rings of white scales which give a banded appearance, Cs. annulata is much larger than Ae. albopictus with a wing span 13 to 15 mm, compared to 7 to 8 mm
2. Cs. annulata also have clusters of scales on their wings which make them look spotted; this does not occur on the wings of Ae. albopictus
3. the thorax of Ae. albopictus has a single white central line from front to back; this does not occur on Cs. annulata

There are 2 important differences between Ae. geniculatus and Ae. albopictus:

1. the bright white scales on a black body of Ae. albopictus can also be confused with similar bright white scales on Ae. geniculatus; however, the latter differs in that tarsi on the legs are not banded, except for a white tip to the femurs (appearing as white ‘knees’)
2. the thorax on Ae. geniculatus has many white lines, and not just a central line as in Ae. albopictus