Flies — Order Diptera

The Arctic is the world’s "fly" zone. It is here, like nowhere else on the planet, that these two-winged insects dominate. In some places, over 50% of arctic insect species are dipterans. Most of these are small, nimble fliers that are difficult to distinguish from one another with the naked eye. Visitors to the southern tundra cannot help but notice the profusion of flies – the clouds of mosquitoes are so thick that it is difficult to eat a meal without swallowing some. But it is only a few, exceedingly abundant species that are responsible for this plague.

Less annoying, but certainly no less important, are hundreds of other flies that do not suck blood. They are, in many respects, the foundation for both terrestrial and aquatic ecosystems. Many are important herbivores and detritivores, contributing to the recycling of nutrients. In the High Arctic, flies are the chief agents of plant pollination, particularly the muscids (house-fly relatives) and dance flies. Many animals that occupy arctic terrestrial and freshwater habitats rely heavily, if not exclusively, on flies for food.



 More than 720 species of flies have been described so far from the Arctic, about 150 of which reach the High Arctic. A few families are particularly well represented in the north – most notably the non-biting midges (Chironomidae), the crane flies (Tipulidae), and the house-fly groups. Like mosquitoes, blackflies, midges, and crane flies, numerous other families spend their juvenile stages in lakes and rivers.

Mosquitoes and blackflies

Mosquito.

The few species of mosquitoes that inhabit the Arctic are abundant and widespread. Two in particular, Aedes impiger and A. nigripes, are not only dominant throughout the southern Arctic, but breed as far north as the High Arctic. Mosquito eggs are laid near the margins of lakes, ponds, or puddles, and the larvae live in these waters, with their tails in the air, taking up oxygen. The "wrigglers" filter feed particles out of the water. Mosquito adults are small, delicate flies with long legs; males feed on nectar, or not at all, while females supplement their diet with a meal of blood. Using straw-like mouthparts, female mosquitoes can consume 1-5 times their body weight in blood, and they use this excellent source of protein to develop their eggs. In the High Arctic, blood supplies are scarce, but arctic mosquitoes have the ability to develop their eggs without a blood meal. Instead, they use protein that had been acquired and saved during their larval stage. When they get the chance, High Arctic mosquitoes still bite birds and mammals – including humans – and one study has shown that muskoxen are the most likely victims on Ellesmere Island.

Blackflies are smaller than mosquitoes, with more compact bodies. Their larvae are specialized for life in fast-flowing water. The larvae anchor themselves to rocks at the bottom of rivers with a ring of hooks and silk safety ropes. Positioned thus, they absorb oxygen through their skin, and sweep particles from the water with their mouth brushes. When mature, the adults ride to the surface in a bubble, and take to the wing. Both males and females feed on nectar, but females also use their saw-like mouthparts to slice open the skin of birds or mammals and lap up the blood that seeps out. Most blackfly species do not have ranges that extend far into the tundra, but the ones that do mature their eggs without a blood meal. Consequently, the residents of the High Arctic are spared annoyance from both biting mosquitoes and blackflies. Both groups of flies also have representatives that have adapted to the harsh arctic environment by doing away with flight in order to find mates. Instead, these species walk across the tundra in search of a partner, avoiding the winds.


Chironomid.

Midges

There are several families of flies that bear the common name of midge – all are characterized by their small size and delicate body form with longish legs and wings. The most important of these families is the Chironomidae, the non-biting midges, with over 140 species recognized from Arctic Canada. In the harshest areas of the Arctic, these flies comprise 50% of all insects! Most species have strictly aquatic larvae, but a few species occupy an unusual, moist environment – they live beneath piles of muskox dung! The aquatic larvae are worm-like, with small heads, and move with whip-like movements. Some species are called bloodworms, a reference to their red colour which indicates the presence of haemoglobin, an oxygen-carrying protein. Most chironomid larve are consumers of detritus, but some eat algae and a few are predacious. Many arctic species are quite long-lived, surviving through the freezing and thawing of arctic ponds and lakes for upward of six years, then taking flight in their adult form for just a few weeks. The adults of some species lack mouthparts altogether and do not feed.

Midges are extremely important in arctic ecosystems. For example, midge larvae are the staple food of arctic charr in High Arctic lakes, as well as numerous birds, especially waders. Some adult midges are important pollinators, and they occur in such abundance that they also form the lion’s share of the diet of spiders and other invertebrate predators.


Others

Besides mosquitoes, blackflies, and non-miting midges, there are 29 other families of arctic flies. Crane flies (Family Tipulidae) are large and conspicuous with extraordinarily long legs. Adult crane flies lack mouthparts and, consequently, never eat. Their larvae are aquatic and numerous. Both life stages are an important food item for birds, comprising virtually the entire diet for sandpipers and phalaropes during their nesting period. Larvae in the genus Prionocera are common inhabitants of submerged and waterlogged moss.

Another long-legged family of flies, the danceflies (Family Empidae), is so named because the males of most species assemble in swarms. Females entering the swarm choose a mate, sometimes based on the quality of a gift – generally a dead fly. Dance flies are even found in the extreme reaches of the Arctic. Hover flies, which have amazing flight capabilities that allow them to hover in mid air, are predatory as larvae and prey on aphids.

Larvae of the botfly, Cephenemyia trompe.

Arctic plants are host to numerous flies that feed on them. The leaf-miners (Family Agromyzidae), have tiny larvae that, as their name suggests, tunnel through the leaves of various grasses, sedges, and other plants, feeding on the cells. These "miners" are not too careful about covering their tracks, as a tunneling leaf-miner leaves a conspicuous network of silver trails behind it. By contrast, the larvae of some flies in the family Anthomyiidae – better known as root maggots – live underground, feeding on the roots of plants. Many flies feed on nectar as adults, including those of the leaf-miners and root maggots, as well as numerous other, house-fly-like insects. There are also dung flies and blowflies that, as larvae, feed on decaying matter. One blowfly from the High Arctic, Boreellus atriceps, consumes decaying corpses.


Some flies have a taste for fresh meat, including two arctic blowflies. Protophormia terraenovae causes wounds in caribou, while Protocalliphora sapphira feeds on baby birds. The botfly, Cephenemyia trompe (Family Oestridae), prefers to munch on caribou noses. This fly attacks caribou, with females releasing their tiny young in its nostrils. These larvae migrate to the base of the caribou’s throat, and remain there in a wriggly mass, feeding on mucous, for the winter. When the warm weather returns, and it is safe to exit, a sneezing and coughing caribou expels the maggots and they drop to the ground to pupate. Their adults are large and hairy, much like their relative, the caribou warble fly, Hypoderma tarandi, which has a distinctively disgusting method of obtaining a meal of flesh and is the subject of the species close-up.
Botfly larvae in the nasal cavity of a caribou.