Saskatchewan Mayflies (Ephemeroptera)

Adult mayflies are relatively uniform in appearance. They range from 5 mm to 3 cm long, with one or two pairs of triangular wings (the front wing is the largest) and two or three long tails or caudal filaments. The adults usually have clear wings with distinct venation. The subadults, or subimagoes, have cloudy wings.

Larval mayflies range in size from about one cm to 3 cm or more. They vary greatly in appearance from stream-lined swimmers to frilly-gilled burrowers and flattened rock-huggers. Their appearance can be quite striking with contrasting color patterns of pale yellow and dark brown to tinges of orange. The unifying feature is the series of abdominal gills variously modified as plates or feathery gills. There can be two or three tail filaments.

Ephemeroptera are found throughout the world except Antarctica. Currently twenty families are reported from Canada represented approximately 326 species. The Saskatchewan fauna is made up of over 110 species belonging to 18 families.

The greatest diversity of mayflies is found in cool rivers and streams. A number of species inhabit lakes particularly those with wave washed, rocky shorelines and cold water. In warm prairie sloughs and potholes only three species have been recorded. Generally mayflies require unpolluted, well-oxygenated, cool water to survive. This makes many mayfly communities useful indicators of ecosystem health. In many habitats they are important fish food, as "fly fishermen" will attest.

The life cycle of mayflies is unique among hemimetabolous insects in that larvae emerge into a short-lived, usually sexually immature, subimago or sub-adult stage. This stage is followed by another moult into the sexually mature adult. The mayfly adult typically survives for only a few hours, just long enough to mate and lay eggs. The adults have no functional gut and in one species, Lachlania saskatchewanensis, females lack functional legs. The adults are often seen flying in mating swarms. Males have a pair of claspers on the end of their abdomen to grasp the female's abdomen for copulation and often have large eyes relative to the females.

Females lay their eggs by flying low over the water surface and dipping an extruded egg sac into the water. In some species, that inhabit swift flowing water, the female will crawl under the water surface to lay her eggs irectly on submerged rocks. The duration of the egg stage can range from a few days to a number of months. Larvae undergo a number of instars (growth stages) depending on species and conditions. In Saskatchewan the length of the life cycle varies from one generation per year (univoltine) to two or more years to complete a single generation (semivoltine).

Larval mayflies exhibit many interesting body forms. Ephemeridae have large frontal tusks and burrow into the soft substrate of lakes and rivers. In rivers and streams some species have streamlined bodies to swim through the current. Others, members of the Heptageniidae, are flattened and cling to rocks to avoid swept away by the current. This has reached the ultimate level in the genus Rithrogena that have gills modified to act as a suction cup to hold the larvae on the rocks.

Larvae are the only feeding stage of the life cycle. In general, larvae feed by collecting or scraping bits of detritus and algae from the bottom, rocks, wood or plants. A few, Acanthametropus, Analetris, Anepeorus, Raptoheptagenia, have adapted to feeding on other aquatic insects. Others, Ametropus, Isonychia and Arthroplea have specialized mouthparts to filter food particles from the water current.

If conditions are favourable large numbers of larvae to synchronously reach maturity an impressive mass emergence of hundreds of thousands of subimagoes and swarms of adults may occur. Along certain areas of the Saskatchewan River Ephoron album can emerge in huge numbers to create the illusion of a blizzard at dusk around bridge lights and ferries during August. In the morning all that remains are banks of dead adults under light standards. Similar mass emergences of other species can occur at lakes and ponds around the province.

Rare Saskatchewan Mayflies:

While some mayflies seem to be flourishing the populations of other species are declining making them extremely rare or possibly extinct and their known habitats should be protected. In a taxonomic survey of Saskatchewan mayflies, Webb (2002), recorded eleven species that were rarely collected: Analetris eximia, Apobaetis indeprensus, Baetis hudsonicus, Cercobrachys cree, Acanthomola pubescens, Anepeorus rusticus, Heptagenia adaequata, Macdunnoa nipawinia, Asioplax corpulenta/edmundsi, Lachlania saskatchewanensis, and Parameletus chelifer. Of these Webb considered A. indeprensus, B. hudsonicus and P. chelifer as not rare because they have been under collected due to sampling methods or inadequate sampling of their habitats and/or ranges. A. corpulenta is possibly a synonym of the widely collected A. edmundsi. H. adaequata and C. cree have only just been recently described so their status is uncertain.

The remaining five species; A. eximia, Ac. pubescens, An. rusticus, M. nipawinia, and L. saskatchewanensis , are likely truly rare in the sense that they are known from only a few localities and although these locations have been regularly sampled the numbers collected are extremely low suggesting the populations are small. The habitats these species are found in are also threatened by dams and increased pollution (Webb 2002).

A. eximia has a rank of G3 (SK Conservation Data Center (CDC) website). It has been collected in the Powder River, MT (Kurtz 2006) and from the Milk River in MT and AB (Webb 2002) as well as the Athabasca River in AB (Barton 1980). It has also been recorded from UT and WY (Patrick 2002). In SK it has been collected from the N. SK River at Borden Bridge and the S. SK River at Lemsford Ferry (Lehmkuhl 1976, Webb 2002). Larval specimens were collected from deep, rapid water over sandy substrates from late May to Oct (Webb 2002) or from post flood backwaters (Lehmkhul 1976). This species is carnivorous, feeding on chironomid larvae (Lehmkuhl 1976) and probably other small insect larvae.

Ac. pubescens has yet to be given a conservation status. It is only known as larvae from two localities, the South SK River in SK at Lemsford Ferry, the Athabasca River in AB (Whiting and Lehmkuhl 1987a) plus a site in MB (Patrick 2002). It is possible this species may be the undescribed larva of An. rusticus. No reports of collections of Ac. pubescens have been made in 20 years (Webb 2002). In the S. SK River larvae were collected in silty rapid current (Whiting and Lehmkuhl 1987a). Due to the rarity of collections any life history information is speculative. It is thought the eggs hatch in May and adult emergence occurs from July to Sep (Webb 2002).

An. rusticus is ranked as G1 (Kurtz 2006). It has been reported from SK, CO and UT (Patrick 2002). This species is known from five adult specimens from SK and AB and pieces of a sixth from UT (Webb 2002). The larva is unknown after larvae attributed to An. rusticus were reared successfully to a new genus/species Raptoheptagenia cruentata (Whiting and Lehmkuhl 1987b). It is now suggested that the larvae identified as Ac. pubescens may be the immature stage of this species (Webb 2002). The adults from SK were collected in September. The type specimen of An. rusticus was collected from Saskatoon, SK prior to 1925. No verifiable specimens have been collected of this species for 80 years (Webb 2002).

M. nipawinia has been given a G2/G3 ranking (CDC website). Collections of this species have been made from S. SK River at Lemsford Ferry in SK and from the Milk River in Montana (Lehmkuhl 1979, Webb 2002). It may also occur in the Milk River of AB and in MB (Patrick 2002, Webb 2002). The larvae have been found attached to snags in fast current (Lehmkuhl 1979, Webb 2002). Larvae were found in collections in early spring with the adults emerging from late June until early August (Lehmkuhl 1979, Webb 2002).

L. saskatchewanensis is ranked as G4 (CDC website). It is known from SK, Mexico, AZ CO, MT NE, NM and UT (Patrick 2002). Although it has a relatively wide distribution through the mid western US and Canada, hence its low ranking, it is rare in collections (Webb 2002). In Saskatchewan it has been collected from the N. SK River at Cecil Ferry and upstream of Lake Diefenbaker on the S. SK River at Lemsford Ferry (Webb 2002). Larvae were found in fast current attached to willow root snags from July to Sep (Webb 2002). Webb (2002) suggests that the numbers of this species in the S. SK River has declined since the 1970’s.

All the above five species have large, western North American, prairie rivers as a preferred habitat. There is evidence, from common faunal components, the large rivers and tributaries which make up the SK drainage and Colorado drainage, were closely associated if not physically connected by the glacial melt water spill ways that developed during glacial recession (Lehmkuhl 1980). As the flows glacial melt water subsided and postglacial climatic changes occurred these drainages, and therefore the populations, are now separated by a 1500 km barrier (Lehmkuhl 1980). Thus the present distributions of these species are relics.

Large prairie rivers are one of the most utilized aquatic habitats in North America. All have been impounded for agricultural irrigation, urban water supplies and hydroelectric purposes. Not only does this alter the flow regime and silt loads of the river, but it also changes thermal patterns down stream from the dams resulting in biologically significant temperature changes (Lehmkuhl 1972). These alterations coupled with large influxes of agricultural, industrial and urban contaminants have resulted in a significant decline in the quantity and quality of the water flowing through these rivers (Edmunds et al 1976). Since most mayflies, especially the species in question, are intolerant of such impacts many populations have become extinct thus fragmenting the distributions of these species further.

At present the S. SK River upstream from Lake Diefenbaker is considered one of the last relatively pristine sections of large prairie rivers left in North America (Webb 2002). It is the one location that all the “rare” species in question have been collected in SK and possibly NA (Webb 2002). Anecdotal evidence over the last 20 or 30 years suggests the quality and quantity of water in this stretch of river has declined possibly endangering the mayfly species in question and the macroinvertebrate community structure they require (Webb 2002). Proposed developments including a dam on the Oldman River, intensive agriculture (i.e. cattle feed lots), irrigation i.e. (vegetable and crop production) and increased urban developments will only increase the impacts on the S. SK river and reduce the quality and quantity of the water.

Below is a larval key to the families of mayflies found in Saskatchewan. It has been modified from Webb (2002). An interactive pdf version of the key is available by emailing me and requesting a copy.

1a: Top part of mesothorax (mesonotum)Arrow indicates shield-like mesonotum. is in the form of a large shield that covers the metathorax and first few abdominal segments.--Baetiscidae SK Baetiscidae Distribution Maps

1b: Thoracic segments not extensively modified.--2

2a: Mouth with forward projecting tusk-like Arrow indicates "tusk". structures. Gills ~~~~ on abdomen in two parts (forked) and "feathery".--3

2b: Head without projecting tusks. Gills not feathery.--4

3a: Tusks curved upwardsArrow indicates "tusk"..--Ephemeridae SK Ephemeridae Distribution Maps

3b: Tusks curved downwardsArrow indicates "tusk".. With pointed tooth-like bumps (denticles) on the top surface.--Polymitarcyidae SK Polymitarcyidae Distribution Maps

4a: Second abdominal gill modified into a shieldArrow indicates shield-like gill two. that covers all or almost all of the remaining gills of the abdomen.--5

4b: Second gill similar to the other gills on the abdomen or not present.--6

5a: Second gill square-shaped~~~. Almost meeting at the center line. First gill a thin filament.--Caenidae SK Caenidae Distribution Maps

5b: Second gill triangle-shaped~~~~~~~. Held more on the side of the abdomen. First gill absent.--Leptohyphidae SK Leptohyphidae Distribution Maps

6a: Second abdominal gill absent.--Ephemerellidae SK Ephemerellidae Distribution Maps

6b: Second abdominal gill present.--7

7a: Maxillary palps extending beyond the sides of the head. They are covered in a fringe of long "hairs" or setae. Found in extreme northern SK.--Arthropleidae SK Arthropleidae Distribution Maps

7b: Maxillary palps not as above.--8

8a: Foreleg with claws forked in two~~~~~~~~.--Metretopodidae SK Metretopodidae Distribution Maps

8b: Foreleg claws simple~~~~~~~~. May have a small spur but never subequally bifid.--9

9a: Head wide and flat~~~~~~~~. Eyes on top of the head.--10

9b: Head more rounded~~~~~~~~, not flat. Eyes on the sides of the head.--11

10a: Claws on legs are all long. As long as tarsi.--Pseudironidae SK Pseudironidae Distribution Maps

10b: Claws on legs very much shorter than tarsi.--Heptageniidae SK Heptageniidae Distribution Maps

11a: Forelegs similar to other legs in appearance.--13

11b: Forelegs (femora and tibiae) with long hairs (setae)Arrow indicates setae. on under (ventral) surface.--12

12a: Two tail filaments at the end of the abdomen.--Oligoneuridae SK Oligoneuridae Distribution Maps

12b: Three tail filaments present.--Isonychiidae SK Isonychiidae Distribution Maps

13a: Foreleg claws much shorter than claws on the other two pairs of legs.--Ametropodidae SK Ametropodidae Distribution Maps

13b: All legs have similarly shaped claws.--14

14a: Gills on abdomen all forked~~~. Both forks similar in appearance.--Leptophlebiidae SK Leptophlebiidae Distribution Maps

14b: Gills different from above.--15

15a: Gills with a brown band~~~ along the side margin.--Ameletidae SK Ameletidae Distribution Maps

15b: Gills without brown band. Uniform in color and appearance.--16

16a: Labrum, the upper lip, usually with a notch in middleArrow indicates notch on labrum. in it. If notch is absent antennae longer than head.--Baetidae SK Baetidae Distribution Maps

16b: Labrum without a notch and antennae shorter than head.--17

17a: Hind claws only slightly shorter than hind tarsi. Found only in the Saskatchewan River system in SK.--Acanthametropodidae SK Acanthametropodidae Distribution Maps (This family is rarely collected due it being found in large river sandy habitats and its sensitivity to habitat changes. Likely should be considered endangered or at risk in SK (Webb 2002).

17b: Hind claws much shorter than hind tarsi. Found throughout SK.--Siphlonuridae SK Siphlonuridae Distribution Maps

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Saskatchewan species list to mayflies (Ephemeroptera):

The species list below is primarily from Webb 2002.

References

Barton, D. R. 1980. Observations on the life histories and biology of Ephemeroptera and Plecoptera in Northeastern Alberta. Aquatic Insects 2:97-111

Conservation Data Center Website, Accessed Nov 30 2008, http://www.biodiversity.sk.ca/

Edmunds, G. F. Jr, S. L. Jensen and L. Berner. 1976. The mayflies of North and central America. University of Minnesota Press, Minneapolis.

Kurtz, C. 2006. The Powder River: Montana’s Last Best? Montana Naturalist Fall: 14-15.

Lehmkuhl, D. M. 1980. Temporal and spatial changes in the Canadian insect fauna: Patterns and explanation the Prairies. Can. Ent. 112:1145-1159.

Lehmkuhl, D. M. 1979. A new genus and species of Heptageniidae (Ephemeroptera) from western Canada. Can. Ent. 111:859-862.

Lehmkuhl, D. M. 1976. Additions to the taxonomy, zoogeography, and biology of Analetris eximia (Acanthometropodidae: Siphlonuridae: Ephemeroptera). Can. Ent. 108:199-207.

Lehmkuhl, D. M. 1972. Change in thermal regime as a cause of reduction of benthic fauna downstream of a reservoir. J. Fish. Res. Bd. Canada 29:1329-1332.

Lehmkuhl, D.M. 1970. Mayflies in the South Saskatchewan River: pollution indicators. Blue Jay 28:183-186.

McCafferty, W.P. and R.P.Randolph. 1998. Canada mayflies: A faunistic compendium. Proc. Ent. Soc. Ontario. 129:47-97.

Patrick, R. 2002. Atlas and biogeographical review of the North American mayflies (Ephemeroptera). PhD. Dissertation. Department of Entomology, Purdue University.

Waltz, R.D. and S.K. Burian. 2008. Chapter 11. Ephemeroptera. In. Merritt R.W. and K.W. Cummins. Ed. An Introduction to the Aquatic Insects of North America. 4th Edition. Kendall/Hunt Publishing Co. Dubuque, Iowa.

Webb, J.M. 2002. The mayflies of Saskatchewan. MSc. Thesis. University of Saskatchewan, Saskatoon, Saskatchewan.430 pp.

Webb JM, Sun LL, McCafferty WP, Ferris VR. 2007. A new species and new synonym in Heptagenia Walsh (Ephemeroptera: Heptageniidae: Heptageniinae) based on molecular and morphological evidence. 16pp. Journal of Insect Science 7:63, available online: insectscience.org/7.63

Webb, J., D.W. Parker, D.M.Lehmkuhl, and W.P. McCafferty. 2004. Additions and emendations to the mayfly (Ephemeroptera) fauna of Saskatchewan, Canada. Ent. News 115:213-218

Whiting, E. R. and D. M. Lehmkuhl. 1987a. Acanthomola pubescens, a new genus and species of Heptageniidae (Ephemeroptera) from western Canada. Can. Ent. 409-417.

Whiting, E. R. and D. M. Lehmkuhl. 1987b. Raptoheptagenia cruentata, gen. nov. (Ephemeroptera: Heptageniidae), new association of the larva previously thought to be Anepeorus with the adult of Heptagenia cruentata Walsh Can. Ent. 405-407.