Saskatchewan Aquatic Two-winged Flies (Diptera)
Adult flies have one pair of wings and a pair of little balancing halteres. Beyond this unifying feature there is a great diversity of body types and structures in the adult and larval stages. Larvae usually have elongated bodies, with or without a distinct head and, although they lack true legs, prolegs MAY be present.
The order Diptera is the most diverse order of insects found in aquatic habitats. Over 5100 species in 30 families are reported in North America as having aquatic stages. In Saskatchewan there are aquatic members of at least 16 families. Unfortunately species lists for families, other than the biting flies, are in an extremely preliminary state or do not exist due to lack of study in the province.
Diptera have four stages in their life cycle: egg, larva, pupa and adult. The length of each stage is species dependent. The egg stage can last from a few days to a number of weeks. The larval stage consists of four or more instars the duration of which can be from a few days to years. This is followed by pupal and adult stages which last from a couple of days to months. The time required to complete the life cycle varies greatly among the species of the order and depends to a large extent on environmental conditions.
The large number of species in the order is reflected in the variety of microhabitats the larvae live in and the feeding methods exhibited. Fly larvae can be found in all types of aquatic habitats from rivers and streams to lakes, temporary ponds and saline lakes. Some can inhabit grossly polluted habitats such as sewage lagoons and pit toilets (members of the Syrphidae). The black flies (Simuliidae) live in running water where they attach themselves to rocks or branches and use specially adapted labral fans to filter small particles from the water. Most mosquitoes (Culicidae) also feed by filtering the water column but they are more typical of shallow standing water. Members of the families Syrphidae, Tipulidae and many species of Chironomidae feed on decaying organic matter. A number of families (Chironomidae, Culicidae, Ceratopogonidae and Tabanidae) have predatory species that feed on other insects and invertebrates either by engulfing the prey whole or piercing the skin and sucking out the body fluids. The larvae of the Sciomyzidae or "snail killers" live as parasites on snails and clams.
As adults Diptera feed on a wide variety of foods such as nectar, fungi, decaying vegetation and flesh. The public is likely most familiar with the blood feeding of the biting flies (mosquitoes, black flies, no-see-ums, deerflies and horseflies). The females of these groups require a blood meal for egg development.
Gas exchange for most larvae living in running water and many in standing water is through the integument. Many larvae inhabiting standing water breathe through spiracles that they bring in contact with the air at regular intervals. While this restricts the depths at which these larvae can live it also allows them to live in extremely polluted and anoxic conditions. Some members of the Chironomidae, commonly called "blood worms", have developed haemoglobin that is extremely efficient in trapping oxygen. This allows these species to live in the bottom mud of deep lakes where oxygen levels are very low.
Below is a family key to the larvae of commonly collected flies found in aquatic habitats in Saskatchewan. The key has been modified from Clifford (1991).
1a: Larvae with an obvious head.--Go to 2
1b: Larvae appear to be headless.--Go to 14
2a: Parts of labrum developed into fan-like structures for filtering out particles from water currents. Last two or three body segments enlarged to give the larvae a bottle appearance. End of body has a hold fast attachment structure. First body segment has a proleg.--Simuliidae (Black flies)
2b: Larvae not as above.--3
3b: Larvae not as above.--5
4a: Two pairs of prolegs. Body ending in hairs and lobes. Often at water surface.--Dixidae
4b: Three pairs of prolegs present. Body ending in a breathing tube that may be retracted. Body covered by rows of rough tubercles and typically rusty coloured.--Ptychopteridae (False Crane Flies)
5a: Several body segments with pairs of prolegs.--Some Tipulidae (Crane Flies)
5b: Larval body without prolegs, or with prolegs only on the first body segment, or with prolegs on the first and last body segments.--6
6a: Prolegs present on the first body segment and sometimes on last body segment as well.--7
6b:Prolegs absent or in a few cases small posterior ones.--8
7a: Body setae obvious.--Some Ceratopogonidae (Biting midges)
8a: First three body segments (thoracic segments) fused and enlarged relative to the other body segments.--9
8b: Body segments not differing significantly in size.--10
9b: Two silvery organs visible in anterior and posterior segments. In life body is transparent. Preserved specimens are usually white. Antennae in most species developed into a grasping structure.--Chaoboridae (Phantom midges)
10a: Small clawed prolegs present on last body segment.--Some Ceratopogonidae (Biting midges)
10b: Prolegs absent.--11
11b: Not as above. More robust.--12
12a: Posterior end with short siphon. Body segments divided into two or three subdivisions which often have individual plates on them.--Psychodidae (Moth flies)
12b: Not as above--13
13a: Body relatively hard, leathery. Dorsoventrally flattened somewhat. Posterior end often with hairs on it.--Stratiomyidae (Soldier flies)
13b: Body soft and fleshy, sometimes covered by fine hairs. Head may be retracted into the body. Posterior end with various lobes surrounding dark breathing holes (spiracles).--Some Tipulidae (Crane Flies)
14a: Body has relatively stiff tubercles and small prolegs on all body segments starting from the third segment.--Athericidae (Snipe flies)
14b: Body structures not as above.--15
15a: End of body has four lobes.--Dolichopodidae (Long-legged flies)
15b: Not as above.--16
16b: Body differs from above.--17
17a: End of body has a long breathing tube(s).--18
17b: Body without long breathing tubes(s).19
18a: One or a split breathing tube at the end of body. Usually not as long as body.--Ephydridae (Shore flies)
18b: Breathing tube is usually as long or longer than body when fully extended. Front end of larva blunt. Body sometimes has a fuzzy appearance. Often found in very organically enriched habitats.--Syrphidae (Flower flies)
19a: Body very fleshy. Usually extremely wrinkled and distorted when preserved. Blunt body tubercles may be present.--Sciomyzidae (Snail killing flies)
19b: Prolegs present on most abdominal segments. In the most common forms end of body usually with a blunt forked process.--Empididae (Dance flies)
About fifty species of mosquitoes have been recorded from Saskatchewan. The female mosquito is the only stage that "bites". Most require a blood meal to produce a full compliment of eggs. However, not all species feast on human/mammalian blood. There are a number of species that prefer birds, reptiles or amphibians. They will also feed on nectar, as do the males. Over the past few years West Nile Virus has been in the news and of great public concern. The main human vector for the virus in Saskatchewan is Culex tarsalis.
People are well acquainted with female mosquitoes but rarely notice the males unless they are in mating swarms. The sexes can be easily distinguished. Both have densely scaled bodies, legs and wings. The females have a long proboscis and sparsely haired antennae. The males have a proboscis, bushy antennae, tufted palpi and the end of the abdomen is modified into external genitalia.
The life cycle includes four stages; egg, larva, pupa and adult. Eggs are laid directly into the water or in damp soil in groups or singly. In many species the egg has a "resting stage" known as diapause that prevents the eggs from hatching until the following spring. Other species have more than one generation a year. Some have desiccation resistant eggs that enable them to withstand consecutive years of drought. Such adaptations enable mosquitoes to successfully inhabit shallow depressions that hold water for only a short period of time at irregular intervals such as ditches and temporary ponds, even old tires and discarded coffee cups may surfice. The eggs hatch into larvae commonly called "wigglers" which describes their characteristic method of swimming. Most mosquitoes feed on microscopic algae and small organic particles that they filter from the water. Larvae pass through 4 growth stages (instars) and then turn into pupae. The pupal stage is a period of major tissue reorganization as the adult body structures develop within it. When the pupal stage ends it swims to the water surface and a split develops along the top of the skin and the adult emerges and flies away.
The family Chironomidae is one of the most important and diverse groups of aquatic insects found in Saskatchewan. Over 190 species of Chironomidae have been reported from the province even though they have been intensively studied in only a very small number of habitats. Larvae can be found in almost every type of water in the province. Some habitats have 80 to 100 species and the larvae can occur in large numbers, over 100,000 per square meter, if conditions are right. They are important in environomental assessments of developments and contaminats on the aquatic environoments and all life stages are important food for fish, waterfowl and passerine birds.
There are four life stages, larva, pupa and adult. Larval chironomidae are regularly found in the bottom mud (benthos) of lakes and ponds and slower back waters of rivers. Others are found adhering to rocks in flowing waters or mining into dead or living plant tissues. Some are found associated with snails or mayflies and stoneflies. Many genera have red haemoglobin in their bodies giving them their common name "bloodworms". And still others are capable of living in semiaquatic moist microhabitats. The larvae feed on the organisms and decaying material found in the sediments (deposit feeding) or graze on the micorganisms living on rocks, branches and other vegetation. Some groups are carnivorous and feed on small crustaceans and small insect larvae including other chironomids.
Many adult chironomids superficially look like mosquitoes. This has resulted in misidentifications by many people of the swarms of adult chironomids flying over their heads. These are just mating swarms that develop over obvious features such as coloured rocks, signposts, vehicles or people. During periods of mass emergence these mating swarms can become extremely large. The "Bug Zapper" developers have used this misidentification to say that the apparatus is killing thousands of mosquitoes when often the majority of bugs being "zapped" are chironomids. Adult chironomids do not bite and most likely do not even feed during their short life time.
Over thirty species fo blackflies are from the province. They are one of the most persistent blood sucking pests in the northern and north central parts of Saskatchewan during the summer months. The immature stages inhabit all types of running water in the area from the large rivers such as the Saskatchewan River to small beaver dam outflows. Under favourable conditions massive numbers of adults can be produced from these habitats resulting in large areas of the province being infested.
Larvae pass through 6 or 7 instars prior to pupating. They feed on small organic particles that are filtered out of the water column by using highly evolved labral fans. The pupal stage takes about five days or so until the adult emerges. Some species have a single generation per year while others are multivoltine. In the latter species the generation time can be as little as a month in the summer. After mating the female require a blood meal for egg development. Most species seek out mammals or birds for this meal.
The adults of many species of ceratopogonids are tiny, hence their common name, "no-see-ums". They can be nuisances if they occur in numbers. Their bite can be irritating and somewhat painful. Fortunately, the adults are usually very localized in their abundance. Not all ceratopogonids feed on mammals; some "bite" other, larger insects such as dragonflies. Others prey upon small flies.
The larvae are generally long, skinny and worm-like, 1 to 1.5 cm long, with a small black head. As larvae, they generally are aquatic or at least semi aquatic. Their diet can range from plant material to small invertebrates depending on species.
Unfortunately not much work has been done on the diversity and ecology of ceratopogonids in Saskatchewan and the thirty-five species recorded are likely low.
About forty-one species are known from Saskatchewan. These moderate-sized flies with their appetite for blood and aggressive behaviour make the tabanids a nuisance for all mammals. The blood meal is needed to develop a full compliment of eggs by the female. Adults also feed on nectar and honey dew to obtain energy. Eggs are laid on leaves overhanging water. When the egg mass hatches the larvae slide into the water. The cylindrical larvae live in wet soil or in shallow water. Larvae pass through 5 to 11 instars depending on species. Some are univoltine while others, especially in northern regions, require more than one year to complete their life cycle. Little is known about larval feeding although it appears that some are predatory. Pupation occurs in a small chamber above the water level.
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