A look at the spread of mosquitoes species across the globe.
The impact of climate change on the distribution of pests is an increasingly common topic of conversation. Although it is relatively easy to understand the principle involved – warming temperatures will allow pests to move into previously uninhabited areas – it can be difficult to find examples that demonstrate the phenomenon. The expansion of mosquitoes into colder climates provides a very real example.
Mosquitoes are a pest of significant importance due to the diseases they carry and their impact on human health. Whilst they have the ability to naturally expand their range through flight, they are also readily transported around the world through human activities, so have the potential to rapidly exploit new geographies as they become available.
Perhaps the most notable recent example is that mosquitoes have just been detected in Iceland for the first time. A local couple, 30 kilometres north of Reykjavik (capital of Iceland) spotted a couple of what they thought were strange-looking flies. Suspecting what they were, they contacted the Natural Science Institute of Iceland. An entomologist managed to capture three mosquitoes (two females and a male), identifying them as Culiseta annulata. This species is native to colder climates, ranging from North Africa to northern Siberia, so are able to handle lower temperatures. Given both sexes were present, it is suspected that the species has now become established in Iceland, although further monitoring in spring will be required for confirmation.
Although the appearance of Culiseta annulata in Iceland demonstrates the potential for rapid expansion of mosquito populations, Culiseta annulata is not known as a major vector of disease. However, the recent appearance of two invasive species in the UK – both major vectors of disease – is a significant finding. Aedes aegypti was found at Heathrow airport in 2023 and Aedes albopictus was found at a petrol station in Kent in 2024. Both species are vectors of dengue, chikungunya and Zika, so their presence has caused concern. However, the 300-plus monitoring stations that are now set up across England and Wales have yet to confirm these species have become established.
As much as the focus has been on the potential future spread of mosquitoes due to climate change and human-mediated dispersal, a notable historical example shows the adaptability of mosquitoes. A thriving population of Culex pipiens f. molestus exists in the London Underground. Recent DNA analysis suggests that the molestus variant of Culex pipiens (which bites humans) and the pipiens variant (Culex pipiens form pipiens, which bites birds), separated a few thousand years ago. The researchers hypothesised that it evolved in Mediterranean or Middle East, where it was too dry for the bird-biting variant to exist. The northward spread of the molestus version was limited by temperature and so was confined to the southern Mediterranean.
Although it was undoubtably transported northwards on many occasions through human movement, populations could not become established due to the cold northern winters. The exception was in below-ground sites, protected from the cold. The first records of below-ground populations were recorded in Northern Europe in the 1920s, with the population in the London Underground becoming apparent when residents were bitten whilst sheltering during the World War II air raids.
Mosquito diseases and climate change in Australia
Aedes aegypti is present in Australia, in central and northern Queensland, and is responsible for the occasional dengue outbreak in the region. This mosquito definitely has the potential to spread further south as the climate warms. However, the more immediate concern to health is the extension of the mosquito season in the more temperature areas of Australia. This can occur immediately as mosquito species endemic to a region simply respond to the prevailing conditions.
According to Dr Cameron Webb, the mosquito-borne disease of greatest concern is Ross River fever. Forty or more mosquito species are known to carry the Ross River virus. An increase in mosquito numbers and an increase in the length of the mosquito season will inevitably increase the incidence of Ross River fever.
