Why are there no mosquitos in Iceland, when they live on both sides of Greenland?

Answer

Mosquitos, Culicidae, are true flies, Diptera, that live all over the world. Adult females suck blood from mammals, birds and in some cases reptiles, to get nutrition and proteins. Without blood intake they cannot develop eggs.

They are not found in Iceland, though they are common in neighbouring countries. There are two types in Greenland, Aedes nigripes, which can be found in all coastal regions and Aedes impiger, which is found in Northwest Greenland. In Norway there are 28 species, including Aedes nigripes. In Britain there are also 28 species, but not all the same as in Norway. In neighbouring countries to the East of Iceland, 41 species can be found.

Mosquito larvae live in water. There they feed on micro-organisms and organic material that they sieve from the water. They stay close to the surface and breathe through a siphon pipe. They often choose to live among reeds or near banks where shadows are cast on the water.

The pupae are also submerged close to the surface and breathe through a pipe. Adult mosquitos only live during the summer. Larvae also only live in the summer. Their lifecycle is short and they can have several cycles each year. In cold countries mosquitos hibernate in the pupa stage of their lifecycle, but the pupa stage is short in the summer.

All of the external conditions described above exist in Iceland. The species best suited to survival in Iceland is probably Aedes nigripes. I once found a specimen on board an Icelandair plane at Keflavík Airport. The plane had come from Narsassuaq in Greenland and was en route to Frankfurt in Germany. It is known that mosquitoes can survive in aircraft landing gear for many hours, even where the temperature goes as low as -50°C.

The reasons why mosquitoes have not colonised Iceland, and in particular the Aedes nigripes species, could be the following:

• They have not reached Icelandic soil from the planes they are carried by.
• If they reach Icelandic soil, then they have not found a place to lay their eggs.
• The Aedes nigripes lifecycle does not suit Icelandic conditions.

It is unlikely that the lack of mosquitoes in Iceland can be attributed to their not having come here, nor to the lack of a suitable breeding habitat. The Aedes nigripes mosquito has been found in a plane, as established above. And there are regular flights from both Reykjavík and Akureyri to Greenland. There are many ponds and marshland close at both of these airports.

The reason is probably to be found in Icelandic conditions. In Greenland and Northern Scandinavia, the pupa hibernates beneath ice during the winter, and hatches as a fly as soon as the ice melts. This happens in spring, as polar winters are continuous. Icelandic winters are variable. There can be a sudden rise in temperature in the middle of winter, with a thaw, then the temperature will drop again.

Under these conditions the pupa would hatch. The mosquito would then need to find prey from which to suck blood, then it would need several days for the eggs to mature, to meet a mate and lay the eggs in a pond or marsh. Changes in climate in Iceland are so rapid that the mosquito does not have sufficient time to complete its lifecycle. Under these conditions the pupa would not be mature when temperatures dropped again and ice formed on the ponds.

There are however in Iceland, several other insects that suck blood from mammals, such as lice, fleas, bedbugs and midges. Lice and fleas are parasites with a permanent habitat in hosts or in their habitats. Bedbugs live in human dwellings. Midges, on the other hand, live in the wild in rivers and streams and the adult fly seeks out mammals.

Mosquitoes and midges sense the higher carbon dioxide level in the air surrounding the hosts from which they suck blood. So they are often collected by putting dry ice in a trap as bait. Dry ice is frozen (solid) carbon dioxide which slowly thaws and evaporates.

Translated by Paul Richardson.

Image: HB