Flies (Order Diptera) are the second-most diverse order of insects (Phylum Arthropoda, Class Insecta) in the world, after the beetles. But in our region, flies take the medal for species richness!

There are two species of acrocerid flies, 171 species of anthomyiid flies, four species of anthomyzid flies, 13 species of robber flies, one species of march fly, 13 species of bee flies, 12 species of blow files, one species of carnid fly, 14 species of biting midges, five species of silver flies, five species of phantom flies, 212 species of chironomid non-biting midges, five species of chloropid frit flies, one species of thick-headed fly, 39 species of mosquitoes, one species of dryomyzid orange fly, 34 species of shore flies, 25 species of fanniid flies, 11 species of heleomyzid sun flies, five species of lauxaniid flies, three species of spear-winged flies, three species of stilt-legged flies, 199 species of muscid flies, two species of oestrid flies, one species of grass flies, 22 species of cheese flies, 12 species of big-headed flies, one species of flat-footed fly, 17 species of flesh flies, 33 species of dung flies, two species of window flies, 43 species of marsh flies, 62 species of black flies, 10 species of soldier flies, 139 species of flower flies, 25 species of tabanid flies, 14 species of tephritid flies, eight species of stiletto flies, and one species of awl fly confirmed present in the NWT.

Bombyliidae

Bombyliidae are a diverse group of small to medium-sized flies. Most species are covered with fuzzy hair or colourful scales; some have intricate patterns on their wings.

In the NWT, they are currently known to be from forested parts of the territory.

As larvae, bee flies feed on immature stages of other insects such as bees, solitary wasps, grasshoppers, and moths. Most species seem to specialize on a small number of hosts, although much remains to be learned about host relationships. Females typically hover over patches of ground or near vertical surfaces such as tree trunks where hosts are found and flick their eggs onto the surface or directly into burrows. Most female bee flies have a special chamber near the tip of the abdomen used to collect sand or dust to coat the eggs, which may help disperse the eggs. Larvae hatch rapidly and are initially mobile as they seek out a host. Once they have found one, they become immobile and feed either internally or externally until pupating, killing the host in the process.

Adult bee flies feed on flowers, consuming both pollen and nectar. Species with a long proboscis (mouth part) may visit a wide range of flowers, including those often associated with long-tongued bees. They can feed while hovering and may rapidly visit a series of flowers much like a miniature hummingbird. Other species with a short proboscis must visit flowers with readily accessible nectar; they are particularly fond of yellow and white daisies and asters. More detailed knowledge of the relationships between flowers and bee flies are lacking in most areas, including the NWT.

Adults are most active on warm, sunny days. Males may spend much of their time sitting on open ground, possibly defending territory, or waiting for females. They will fly a short distance in response to disturbance, eventually returning to their original spot. Bee flies spend the winter as either larvae or pupae, although their life cycles are not well known. Canadian species seem to have one generation per year. Some species will only be present as adults for a week each year, while others may be present through most of the summer.

Most of the NWT species are widespread across the Canadian boreal forest. One unnamed species of the genus Systoechus was found at Reindeer Depot near Inuvik, and is currently not known from anywhere else in the world. The status and distribution of most NWT species are poorly known due to limited research.

Calliphoridae

Calliphoridae are among the easiest flies to recognize. Most species have a body partially or entirely metallic blue or green; some are polished black, coppery, or without metallic reflections. They are medium to large flies. Many adults, like those of the familiar greenbottle flies (subfamily Luciliinae), are flower visitors, where they look for plant nectar, or rest on foliage, usually in bright sunlight. Others, like the bluebottles (subfamily Calliphorinae), particularly those of the genus Calliphora, are attracted by fresh or cooked meats and fish. Calliphorids flies can detect odours of decay from quite far away and are able to fly up to twenty kilometers in search of a carcass.

As larvae, most blow flies are scavengers and quickly feed on decaying materials. Those maggots perform a valuable service to humans in helping to remove fecal matter and dead animal from landscapes. However, because of this habit to visit dung and dead matter, some Calliphorids can transmit pathogenic microorganisms.

The timing of development of blowflies is predictable when the surrounding temperature is known. Many species are of great interest in forensic entomology in determining the times of death of a corpse.

In contrast, some species of Calliphoridae can be producers of myiasis (the development of dipteran larvae in a living vertebrate body). Myiasis-producing blow flies are usually attracted to the wounds of humans and domestic animals, where larvae feed on necrotic tissue. Based on this process, maggots of the species Lucilia sericata are now often applied as a treatment of infected wounds, a procedure called maggot debridement therapy (MDT).

Another group of Calliphoridae, the bird blow flies of the genus Protocalliphora, oviposit in bird nests where their larvae suck blood from the nestlings as ectoparasites. The action of those larvae can negatively influence health and survivorship of brood of many birds including ravens (Corvus spp.), and swallows. Others Calliphorids flies, the genus Pollenia (cluster flies) enter houses to overwinter in uninhabited parts, sometimes in large numbers. These flies are neither garbage nor manure-related but parasitoid of earthworms.

There are over 1,525 Calliphorids species distributed all over the world and 62 species are currently recorded in Canada. Of those known to be in the NWT (see the list in the next pages), two, Protophormia atriceps and Calliphora genarum are rare in North America, and are found only in northern Canada and Alaska. In the same way, Lucilia magnicornis is an infrequently collected northern species recorded from Alaska to Labrador.

Sarcophagidae

Sarcophagidae are robust grey and black flies, ranging from 2.5 mm to 20 mm in length. They possess a thorax that usually has three dark stripes and an abdomen that is generally checkered. Adult Sarcophagidae can often be observed basking in the sun on foliage, open ground and the sides of buildings. They have pad-like mouthparts for imbibing liquids like nectar, honeydew, tree sap, and juices from damaged fruits. In contrast to their common name – flesh flies – very few larvae exploit larger vertebrate carrion as a food resource. Many of them show a strong trend for saprophagy, mostly in dead insects and other invertebrates or are parasitoids of live insects.

Flies of the Genera Metopia and Phrosinella (called satellite flies) are cleptoparasites of solitary bees and wasps. They use several strategies to locate their hosts; for example, they trail Sphecid wasps to their nest or search directly for nest entrances. In many cases, the fly larva eats the host egg or larva and feeds on the stored food.

This is a diverse family, and species display a multitude of life habits. Sarcophagidae are mostly beneficial insects. Adults, especially males, visit flowers and some species act as pollinators. Some species, parasites of grasshoppers and locusts, are probably of significance as biological control agents. The species Sarcophaga aldrichi (not currently confirmed in the NWT) is a common parasitoid of many pest Lepidoptera, including the forest tent caterpillar (Malacosoma disstria) and the spruce budworm (Choristoneura fumiferana). Flesh flies also represent a suitable insect for monitoring pollutant groups (e.g. heavy metals, residues of organochlorine pesticides and polychlorinated biphenyls) in various habitats. In this sense, Sarcophagidae used as forensic indicators, i.e., to estimate postmortem intervals, can also be used for the detection of various drugs or toxins present in the remains. Sarcophagids are cosmopolitan in distribution although their numbers decrease rapidly with latitude, with few subarctic species and none living in the treeless tundra. Their diversity is markedly concentrated in tropical regions.

Syrphidae

Syrphidae (called flower flies, hover flies or syrphid) are, true to their name, flower visitors as adults. Some species are among the most adept fliers in the insect world, reminiscent of miniature hummingbirds as they work flowers for their nectar rewards.

Because flower flies are often excellent mimics of bees and wasps, they are harmless but gain protection from predators who mistake them for stinging insects and they are commonly overlooked at flowers. Indeed, many books, advertisements, media articles, and literature extolling the benefits of bees mistakenly illustrate flower flies!

In contrast with the relatively uniform adult ecology of syrphids, larval flower fly ecology is amongst the most varied of any insects. Larvae of some species, e.g., genus Syrphus, are predatory on aphids, scales, and other insects. Many of these species are of critical importance in controlling pest numbers.

The genus Pipiza feed on specialized root aphids, whereas the bizarre ant flies, genus Microdon, are predators and parasitoids of ants. Other flower fly larvae are predators, filter-feeders of bacteria, and excellent indicators of the health of old growth forest ecosystems, as they live in sap that runs under bark, or of aquatic ecosystems, as they live in rivers and wetlands. Some prefer putrid water such as that found around farms or sewage lagoons (this includes the familiar rat-tailed maggots, Eristalis tenax). Species that live in putrid water are often found in the billions and are critical in improving water quality. These species are being investigated for use on a commercial scale in water treatment facilities.

Many species life histories are a mystery. It would be interesting to find out what Volucella arctica does for a living in the NWT. Other Volucella live in bee nests as larvae where they feed on debris as well as bee eggs and larvae.

The most diverse genus of flower flies found in the NWT is Platycheirus, called sedgesitters. Many of these flies have fantastic modifications of the male legs. In these species, specific ‘flags’ are used for sexual display. As the common name implies, many sedgesitters are wetland specialists and can often be seen sitting on sedges and feeding on sedge pollen.

Monitoring Syrphidae can be done with traps such as malaise traps, but the most successful survey work is achieved by learning the group and hand collecting. The best way to find rare species is to look for them at their hill topping sites. Males of most species visit hilltops and other prominent landmarks where they wait for females. Hills need not be large, but the most isolated hills attract the most species. Combining hilltop surveys with flower collecting and some targeted sweeping near wetlands should turn up most of the species in an area.

Chironomidae

Chironomidae (non-biting midges) are a diverse and vital component of freshwater insect fauna, though their significance extends well into the terrestrial habitats. Chironomidae importance in their environment can be explored in terms of food-web contribution, bioindicators, and medical importance. Subfossil remains of Chironomidae larvae in deposits of lakes and ponds reveal thousands of years of environmental change in freshwater and adjacent terrestrial habitats. For example, some forty years of data on Chironomidae species distribution in European alpine regions has been used to demonstrate the climatically driven glacier retreats.

Environmental disturbances such as flooding and drought can cause the local extinction of many fauna, with recolonization often being delayed. Chironomidae are usually among the first colonizers of disturbed environments, especially in vulnerable regions such as the Arctic. This means that periodicity and cycles of environmental disturbance can be traced using the distribution of Chironomids. Their larva and pupa are in most part aquatic, a few are aquatic or terrestrial, and a few species occur in marine environment. Their occurrence in freshwater ranges from temporary habitats such as ditches, potholes, and pitcher plants to springs, streams, rivers, and lakes. Adults are terrestrial and usually are found swarming in the vicinity of waters.

Chironomidae is the most diverse family of Diptera in Canada. Large areas of Canada are covered in freshwater and given that diversity and abundance of Chironomidae usually increases by latitude, it can be expected that northern regions contain a higher portion of this diversity. However, since the Canadian Chironomidae fauna are poorly investigated, a large number of unrecorded and undescribed genera and species remain to be discovered.

Although interest in the Chironomidae of northern region of Canada continues, sadly no current Chironomidae work is carried out in NWT, nor has been carried out for the past four decades. Recent investigations in other northern regions have resulted in many discoveries. Integrating the Chironomidae diversity research into the freshwater ecological and environmental investigation of the Arctic is crucial. Future studies must focus on improving the taxonomy of different life stages of Chironomidae species in the North along with understanding their geographic distribution. This information will help mangers and regulators make more accurate assessment of the health of the northern aquatic ecosystems.

Oestridae

Oestridae (including bot flies and warble flies) are medium-sized to very large, heavy-bodied hairy flies. They have a very short adult life – they don’t eat and live on reserves accumulated during the larval stages. Adults are rarely encountered except at elevated sites and on hilltops where males actively seek for females. Once they reach the summits, the first males strongly chase latecomers. After mating, females attempt to find hosts, which are almost exclusively mammals that they harass, usually by flying around them. Eggs (or the first instars, in some species) are laid very quickly, in flight, usually on the hair of the host’s pelage. As larvae, all Oestridae are obligate parasites in the bodies or tissues of living vertebrates, usually mammals. Their skin, rather thick at late stages, is usually covered with triangular spinules regularly deposited in bands or transverse series along their bodies. Upon reaching maturity, larvae of all species leave the host, fall to the ground and pupate into the soil.

Ostrid flies show a high level of host specificity. The genus Cephenemyia penetrates the nasal cavities and pharynx of Cervids. The reindeer nose botfly (Cephenemyia trompe) will parasitize caribou, deer, moose,  and several other species. Females of this species do not lay eggs but are able to discharge many first instars and to spray them towards the nose, the mouth, or the eye of a host. Those larvae then migrate into the nasal cavities where they feed on mucous. Second and third instars later develop in the pharynx of the host until maturity.

Reindeer warble flies (Hypoderma tarandi) resemble bumble bees, presumably to protect them from natural enemies. The females of species lay a batch of up to 15 eggs on the hairs of Rangifer (caribou and reindeer), on lower body and legs. After hatching, the first instars penetrate the skin and migrate through the body tissues to overwinter. They pursue migration the following spring and move to the back of the host, where they develop in subcutaneous swellings called ‘warbles’, feeding on cellular debris. Mature larvae exit their warbles after 30 to 60 days, fall to the ground and pupate. Adults live only few days. Warbles are traditionally valued for their nutritional qualities in Inuit culture.

Conopidae

Conopidae is a small, rarely collected family of flies. Many species are noted for their mimicry of wasps and bees. Adult female conopids deposit eggs within living hosts, often midflight, using modified abdominal structures. The larvae develop within the host until the host succumbs. Following pupation and overwintering, the adult conopid emerges from the host’s corpse in spring or summer.

Various species of Hymenoptera are reported as hosts to these parasitoids. Conopids are also regularly collected from flowers but their role as pollinators, or even their degree of plant specificity, is poorly understood. The best way to observe conopids is to wait by sunny patches of flowers frequented by bees. Adults of Conopidae are only present for a few weeks in the late spring or summer. Thecophora occidensis is the only species that has been recorded from NWT, and then only from the forested regions in the southwest. This species has been reported from all across Canada and the United States.