FAMILIES OF MAYFLIES (EPHEMEROPTERA) OF
R. A. Cannings and G. G. E. Scudder
Copyright © 2005 - All rights reserved
Key to Families of Ephemeroptera
1. Forewings with base of MP2 and CuA strongly divergent from base of MP1, MP2 strongly bent towards CuA basally (Fig.); hindwings well developed and with numerous longitudinal crossveins; hindwings with MA forked (Fig.) ..................................................................................................Ephemeridae
- Forewings with base of MP2 and CuA not strongly divergent from base of MP1 , (Fig); hindwings sometimes reduced or absent............................................. 2
2. Forewing with cubital intercalaries consisting of a series of veinlets, often forking or sinuate, attaching CuA to hind margins of wing (Fig.)............................... 3
- Forewing with cubital intercalaries not as above (Fig.)........................................ 4
3. Claws of each pair similar and sharp (Fig.); costal projection of hindwings obtuse or weak (Fig.) ..........................................................................Siphlonuridae
- Claws of each pair dissimilar, one sharp and one obtuse (Fig.); costal projection of hindwings acute (Fig.)................................................................... Ameletidae
4. Abdomen terminating in three well developed caudal filaments......................... 5
- Abdomen terminating in two well developed caudal filaments, the median telofilum being rudimentary or absent....................................................................... 7
5. Hindwings present and relatively large, with one or more veins forked; costal projection shorter than wing width (Fig.) .....................................................6
- Hindwings absent ..............................................................................................9
6. Forewing with short basally detached marginal intercalaries between veins along entire outer margin of wings (Fig.); genital claspers of male with one short terminal segment (Fig.)........................................................... Ephemerellidae
- Forewing without short basally detached marginal intercalaries between veins along entire outer margin of wing (Fig.); genital claspers of male with 2 or 3 short terminal segments (Fig.) .........................................................Leptophlebiidae
7. Forewings with short basally detached single or double marginal intercalaries present in each interspace; forewing with MA2 and MP2 detached basally from their respective stems (Fig.); hindwings small or absent; penes of male membranous; upper portion of eyes of male raised on a stalk-like structure (Fig.).............................................................................................. Baetidae
- Forewings with marginal intercalaries attached basally to other veins; forewing with MA2 and MP2 attached basally (Fig.); hindwings relatively large; penes of male well developed; eyes of male not raised on a stalk-like structure................. 8
8. Hind tarsi apparently 4-segmented, the basal tarsomere fused or partially fused to tibia; forewing with one pair of cubital intercalaries (Fig.) .............................................................................................Metretopodidae
- Hind tarsi distinctly 5-segmented; tarsi shorter than tibiae; forewing with two pairs of cubital intercalaries (Fig.) .....................................................Heptageniidae
9. Forewing with MA forming a more or less symmetrical fork, and with MP2 and 1MP extending less than ¾ distance to base of MP (Fig.); genital claspers of male 2 or 3-segmented; thorax usually black or gray.................. Tricorythidae
- Forewing with MA not forming a more or less symmetrical fork, but with MP2 and 1MP almost as long as MP, and extending nearly to base (Fig.); genital claspers of male one segmented; thorax usually brown .......................................................................................................Caenidae
Description of Families
Suborder Furcatergalia (=Retracheata)
The Leptophlebiidae is the dominant mayfly family in South America, Africa and Australia. About 400 species are described from around the world. In North America there are nine genera and 72 species named. Two of these genera, containing 11 species, live in B.C.
The eyes of adult males are distinctly separated into an upper part with large facets and a lower one with small facets. Hindwings are rarely absent. There are no short intercalary veins at the wing margin, but there are two to four long intercalaries between CuA and CuP; the latter vein is strongly recurved. There is no costal projection on the hindwings of B.C. genera. The medium-sized adults are strikingly sexually dimorphic: males are brown, often with the middle abdominal segments pale; females typically are red-brown without white mid-abdominal segments. There are three caudal filaments.
The larval body is flattened to varying degrees, but separated from the Heptageniidae by gill structure, which is variable: gills on segments 1 to 6 or 1 to 7, those on at least 2 to 7 forked, or doubled and ending in a slender process. Three caudal filaments occur, each with a whorl of setae around the apex of each segment.
Larvae feed predominantly on plant material and organic particles gleaned from the sediments. They develop in a wide variety of habitats from ponds and lakes and quiet areas of streams to fast flowing waters. Leptophlebia species prefer quiet areas where silt and debris accumulate. Paraleptophlebia can handle swifter flowing water and is usually found in shallow, gravelly, rather rapid streams, but also lives in larger rivers.
Leptophlebia has slender, forked gills on segment 1; segments 2 to 7 have plate-like, double gills ending in a slender ponted process. The enlarged surface area of these gills is an adaptation to life in quiet and stagnant water with low oxygen levels. Three species are recorded from B.C.: the common L. cupida (Say) and L. nebulosa (Walker) which range all across North America and the western L. gravastella (Eaton), which in B.C. has been collected only at Osoyoos. The only other B.C. genus, Paraleptophlebia, is more diverse, with eight species recorded in the province. Some species (B.C.’s P. bicornuta (McDunnough), for example), has a tusk-like projection on the mandibles. Gills on segments 1 to 7 forked, slender, acute. The rear margin of each the abdominal segment has a row of short spines. P. temporalis McDunnough, a species of coastal mountains from Oregon to at least the B.C. central coast, is one of the most abundant mayflies in coastal streams in southwestern B.C. All the B.C. species except P. debilis (Walker), which is common across the continent, are western mountain species.
Infraorder Scapphodonta (Burrowing Mayflies)
These burrowing mayflies are our largest and most conspicuous species. The family occurs on all continents except Australia; there are about 100 species worldwide. North America has 4 genera containing 15 species; 2 genera, each with a species, are recorded in B.C.
Adults are large, up to 32 mm long (8 cm long if caudal filaments are included). The male’s eyes are moderate to large. The tarsal claws of females, and those on the middle and hindlegs of males are dissimilar; one is blunt, the other sharp. Veins MP2 and CuA in forewing are strongly divergent from MP1 basally. Vein A1 is not forked and is attached to the wing’s hind margin by three or more small veins. The abdomen has two or three caudal filaments.
The larvae have mandibles bearing long, upcurved tusks that project in front of the head. The front of the head has a prominent process of variable shape pointing forward. Abdominal gills on segment 1 are vestigial, on 2 to 7 they are forked and distinctly fringed, curving dorsally over the abdomen. The legs are stout, modified for digging; the tip of hind tibia is pointed and extends past the base of the short tarsus. There are three caudal filaments.
Ephemerid larvae live in lakes and slowly moving streams where they burrow in the bottom sediments. In B.C. most populations probably produce one generation a year, but in some places, members of the family take up to 3 years to develop. The two species in B.C. are Ephemera simulans Walker and Hexagenia limbata Serville.
Larvae of Ephemera species have a forked frontal process and the mandibular tusks have setae mainly on the basal half. The terminal filament in adults of both sexes is as long as the cerci. Larvae burrow in sand and other substrates where the particles are rather large and hard. In lakes, normally the larvae live in shallow water less than a few metres deep and, depending on the species, they are found in the quiet stretches stream habitats ranging from creeks to large rivers. Food varies from species to species, but E. simulans is mainly carnivorous. The adult of E. simulans is about 11 to 13 mm long (without filaments), mostly red-brown with a conspicuous darker pattern on the abdomen; the wings are spotted with dark patches. Mating swarms gather about sunset and last until dark. Records are mostly from the dry interior of the province.
Hexagenia larvae have a rounded frontal process; the tusks have long setae along their length. Burrows are made in softer material than those of Ephemera; fine silt and mud substrates are chosen. Burrows can occur in high densities in shallow water or at depths down to around 18 metres. The larvae often leave their U-shaped burrows to feed on the surface of the mud, but mostly they filter material out of the water from their burrows. H. limbata is our largest mayfly; the adult’s body is about 3 cm long, not including the two long caudal filaments, and is mostly yellow with brown markings. The wings are largely clear with the front edge of the front wing purplish and the outer edge dark. B.C. records are from the large lakes and rivers of the southern Interior, where windrows of exuviae often wash up on shorelines during summer emergences. Mating occurs at dusk in swarms over lakeside vegetation, usually at treetop level.
This cosmopolitan family contains about 85 described species; in North America there are four genera and 26 species. Two species of the genus Caenis are recorded in B.C.
In adults, the eyes of both sexes are small and far apart. The hindwings are absent; the forewings are broad and have few crossveins; veins MP2 and IMP are about as long as vein MP1; the anal area is broad and the hind edge of the wing bears a fringe of setae. There are three caudal filaments -- extremely long in males, short in females. The male’s genital forceps are one-segmented.
The larva has a rather flattened abdomen and, in mature larvae, hindwing pads are absent. Squarish operculate gills on segment 2 cover gills on shortened segments 3 to 6. The edges of these gills are fringed with setae and, in Caenis, the gills on segment 2 are also fringed. Caenis has prominent spine-like projections on the hind corners of the abdominal segments 3 to 6. There are three caudal filaments.
Larvae develop in slow streams, lakeshores and the still waters of ponds and marshes. Caenis is especially common in marshy ponds, where the larvae live among the silt, debris and rooted plants on the bottom. They eat mainly plant material, but frequently scavenge dead animal matter. Caenis adults can shed the subimago exuvia while flying; emergence is often synchronized so that huge numbers appear over ponds and marshes. They live only about two hours. Caenis simulans McDunnough is recorded from the Thompson-Okanagan region. C. youngi Roemhild lives at Liard River Hotsprings in northeastern B. C.
There are about 165 species named in this cosmopolitan family. Until recently Ephemerella was the only genus of the family recognized in North America, but a number of subgenera have been raised to higher rank and there are now 8 genera, with 90 species, listed for the continent. All, but one of these genera are recorded in B.C. and 18 species are known in the province. Of the genera known in North America, Drunella, Ephemerella, Eurylophella and Serratella are distributed in both Eurasia and North America; the others are restricted to North America.
Adults are normally mostly brown and are small to medium-sized (5 to 20 mm long). The male’s compound eyes almost meet on top of the head. The hind tarsi have four segments and the claws are dissimilar on all legs. Forewings have few crossveins along the front of the wing; other crossveins are weak; short intercalary veins lie between long veins along wing margins. The costal projection slightly rounded on hindwing. Males have a single short segment at the tip of the genital forceps; three caudal filaments are present.
Larvae are 5 to 15 mm long, variable in form: some species are slender and streamlined, others are flattened below, arched above, with broad, flat femora. Many have paired tubercles on the top of the head, thorax and abdomen, or on the abdomen only. Gills are absent or rudimentary on segment 1, absent on 2, present or absent on 3; the gills have double lamellae. If there are no gills on segment 3, those on 4 are more or less operculate. The rear corners of the abdominal segments are usually produced into spines.
Ephemerellid mayflies live in many situations, from rapidly flowing creeks to slow rivers and wave-washed lakeshores. They hide in crevices or cling to rocks, roots and moss and graze on diatoms, other algae, detritus and small invertebrates. Adults normally swarm at dusk, sometimes many metres in the air.
Attenella is a strictly North American genus. The larvae have rudimentary gills on segment 1, lack gills on segment 3 and the gills on 4 do not cover the remaining pairs. Most abdominal segments bear pairs of dorsal tubercles. One species is reported in B.C. - A. margarita (Needham); it has separate populations in eastern and western North America (or it has evaded capture in the central parts of the continent). Caudatella is restricted to western mountain regions from B.C. and Alberta south to California and Wyoming. Larvae have gills on segment 3, and paired tubercles on the abdominal segments. In both adults and larvae the terminal filament is much longer than the cerci. All three of the species are recorded in B.C., mostly from the southern Interior; the larvae develop in rocky streams.
Drunella is the largest genus of the family in B.C. with seven species in the province, all of which are restricted to the western mountains of North America. The larvae have gills on segment 3; if the head, thorax and abdomen lack pairs of dorsal tubercles, then the fore femur has tubercles along the front edge. One of the most common species of Ephemerellidae in B.C., D. doddsi (Needham), lacks the dorsal tubercles in the larva; it is distinctive because the underside of the abdomen has an adhesive disc made of long, dense hairs for attaching the larva to rocks in strong currents. Another widespread species, D. coloradensis (Dodds), may swarm in huge numbers 30 metres above the ground. There are three species of Ephemerella recorded in the province; the larvae have gills on segments 3 to 7. Two species, E. inermis Eaton and E. infrequens McDunnough, are western; E. aurivilli Bengtsson ranges across the continent.
Eurylophella larvae have vestigial gills on segment 1, no gills on 3 and the operculate gills on 4 overlap the gills on 5 to 7. There are paired tubercles on the abdominal segments and usually also on the head. E. lodi (Mayo) is the only B.C. species; it is the only western North American species known in an otherwise eastern group. Serratella also has no known transcontinental species. The B.C. species are S. teresa (Traver) and S. tibialis (McDunnough). Mating swarms in the latter species are reported up to 15 metres in the air. The larvae have gills on abdominal segments 3 to 7. Tympanoga contains only one unusual species, T. hecuba. (Needham), which lives on rocks in fast streams in the western mountains. In B.C. it has been collected in the southern Interior. The adult abdomen has long lateral projections on the rear corners of segments 8 and 9 and there are vestigial gills on segments 4 to 7. The larva is flattened and hairy, the head is small with a broad frontal shelf. The abdomen is broad with the sides of the segments extended into long pointed spines; gills on segments 5 to 7 are hidden by the gills on 4.
Family Leptohyphidae (=Tricorythidae)
Probably derived from the Ephemerellidae, the Leptohyphidae is most diverse in Africa; about 125 species are described worldwide. There are two North American genera, Leptohyphes and Tricorythodes; the latter is the most widespread.. Although there are 24 species of Tricorythodes in North America, only one, T. minutus Traver, ranges north to B.C.
Male and female adult leptohyphids have small, widely separated eyes. The hindwings are absent or reduced, and there are three caudal filaments. The moult between the subimago and adult can occur in flight. The larvae have large triangular gills on abdominal segment 2 that do not meet at the midline, but that cover the succeeding pairs of gills. The gills on segments 3 to 6 are simple or bilobed, but not fringed.
Tricorythodes minutus is a small species, 2.5 to 5 mm long, red-brown to dark brown with whitish forewings (hindwings are absent). B.C. records are from the Cariboo, but it is probably more widespread in the province. Mass flights often occur. The larvae prefer moderately or gently flowing streams, and sprawl on silty or sandy substrates or among the submerged roots of plants. They eat algae and detritus.
Once considered a siphlonurid genus, Ameletus has been placed in the Family Ameletidae along with the European Metreletus. The family has about 55 described species. It is distributed across northern Eurasia and North America; in America it ranges south along the Appalachians and western mountains, but it is absent from the centre of the continent. Ameletus has 32 recognized species in North America; 12 of these occur in B.C.
The adults are usually brown or yellow-brown; in some species the crossveins in the front half of the forewing are marked with brown, giving the wing a speckled look. The male’s eyes meet dorsally and its forelegs are nearly as long as the body. The two claws on each tarsus are dissimilar. The costal projection on hindwing is pointed. There are only two caudal filaments.
In the larvae, gills are single, small and oval on segments 1 to 7; those on segment 1 are half the size of the ones on 3 to 5. The gills have a sclerotized band on the outer margin. The three caudal filaments are shorter than the abdomen and usually are banded with dark pigment; a wide band across the middle and a narrow one at the tip are common. These mayflies mostly develop in small, fast-flowing streams (sometimes only a few centimetres wide and one or two deep), but they also live in rivers, lakes, and ponds with clean rocky or gravely bottoms. The larvae swim strongly, feeding on algae and detritus on rocks and among vegetation and debris.
Most of the 12 species from B.C. are reported from one or two localities and probably are much more widespread than the records indicate. This is probably true of A. sparsatus McDunnough, one of the species with brown spotted forewings, which has been recorded only at Oliver in B.C. Although the southern Okanagan Valley is a significant area of species richness in B.C. and Canada, even this species likely lives across the province.
The Baetidae is a large and widespread family found on all continents. Their closest relatives live in the Southern Hemisphere; the closest North American family is the Ameletidae. Although baetids live in all sorts of habitats, many species thrive in cold places – Baetis is usually the only genus of mayflies on the arctic tundra and in the highest mountain streams in Asia and North America.. There are about 520 species worldwide; North America has and 18 genera and 130 species. Six genera and 14 species are recorded in B.C.
The adults are small, usually about 3 to 11 mm long (without caudal filaments). The eyes of males are divided into a large turbinate upper part and a smaller lower section. The venation of the wings is reduced and the hindwings are vestigial or absent. The veins IMA, MA2, IMP and MP2 are basally detached in the forewing; the spaces between the veins along the outer edge of the wing have one or two short intercalary veins. There are only two caudal filaments; the male penes are membranous and retractable.
Baetid larvae are streamlined swimmers much like those of the Siphlonuridae and Ameletidae, but the antennae are usually longer (at least as long as twice the head width) and the abdominal segments generally lack well-developed projections on the rear corners. There are gills on abdominal segments 1 to 7, 1 to 5 or 2 to 7; they vary in structure, and may be doubled or folded, but are never forked.. The labrum has a distinct notch. All tarsal claws are similar. Larvae scrape algae from the substrate or feed on fine detritus and diatoms in surface deposits.
Two species of Acentrella, A. insignificans (McDunnough) and A. turbida (McDunnough) live in the rapids and riffles of fast-flowing, rocky streams in B.C.; both are restricted to western North America. Larvae are flattened and have all femora, tibiae and tarsi edged with a long row of setae. Abdominal segments 1 to 7 bear simple, ovate gills; the caudal filaments are not banded and the middle one is vestigial. Baetis is a large and complex genus with five B.C. species recorded, all western in distribution. They develop mostly in shallow flowing water, although some live along wave-washed lakeshores. B. parallelus Banks is a southwestern U.S. species, known in Canada only from Oliver, probably from the Oknagan River. This is an old record from the 1920s, long before the Okanagan River was diked and deepened. Baetis adult males usually have abdominal segments 2 to 6 clear and pale, the terminal segments dark. In some species, females oviposit under water, attaching the eggs in rows to submerged objects.
Although Callibaetis is a common genus of ponds, ditches and marshy lakeshores, and tolerates a wide range of temperatures and pH, only one species is known from B.C. -- C. americanus Banks. The species ranges widely across North America. Centroptilum species live in a variety of habitats from the sandy bottoms of slow streams to rock surfaces in stream currents to lakeshores. The larvae have three caudal filaments banded with dark pigment every 3 to 5 segments. The inner sides of the gills are usually broader than the outer parts. The adults have small, narrow hindwings with a hooked costal projection. The single species reported from B.C., C. bifurcatum (McDunnough), lives across the southern half of the province.
Diphetor has no gills on abdominal segment 1. D. hageni (Eaton), the only known species in B.C., is obligately parthenogenetic. It lives in the southern Interior of the province. Procleon contains four species in B.C.; they mostly live in standing water or slowly flowing streams. The tips of the larva’s caudal filaments have bristles on the sides.
This small family of two genera ranges across northern Eurasia and North America. There are nine species. Metretopus contains two species in North America. M. borealis Eaton, which is Holarctic in distribution, is the only BC species. Recorded from the Peace River region, it is a brownish species with the middle abdominal segments of the male translucent; the wings are clear. The second genus, Siphloplecton, has seven species in North America; they are mostly eastern in distribution.
Adults are brown, often with pale markings, and 10 to 15 mm long. Forewings Have one or two pairs of intercalary veins between CuA and CuP (Metretopus has one, Siphloplecton has two); stigmatic crossveins (those on front edge of wing near tip) tend to form a network.. The male fore tarsus is three times as long as the tibia; the hind tarsus has four segments and the claws are dissimilar. There are only two caudal filaments.
The larval body is slender and minnow-like. All tarsi are longer than the tibiae. The claws on the forelegs are forked, those on the mid and hindlegs are long and pointed and longer than the tibiae. Oval gills are present on segments 1 to 7; they are single on Metretopus, but are double on segments 1 to 2 or 1 to 3 in Siphloplecton. Long setae line the inner edges of the cerci and both sides of the terminal filament.
Larvae of the Metretopodidae live in slowly moving streams and rivers, although Siphloplecton also has been collected from deep and shallow sites in lakes. Little is known about the habits of Metretopus, although judging from the structure of the larva, it is a good swimmer and probably behaves like members of the related Siphlonuridae. Long claws are an adaptation to living in sand; perhaps this is the predominant substrate where the larvae live.
Most species of Siphlonuridae develop in cool water and come from the temperate zones of the Northern and Southern hemispheres. There are about 70 species worldwide. North America contains four genera and 25 species, but B.C. has only two genera and four species.
Adult siphlonurids have many veins and crossveins in their wings; the forewings are rather narrow and triangular, the hindwings relatively large. In B.C. species the hindwings are less than half as long as the forewings and the costal projection is broadly rounded. Vein CuA is attached to the rear edge of the wing by veinlets; the forks of veins MP and CuA are more or less symmetrical. The male’s eyes are not highly modified; they usually meet on top of the head and the facets on the upper part are larger than those on the lower part. There are two caudal filaments; the terminal filament is a stub.
Larvae are streamlined and minnow-like and are active swimmers when disturbed. Their head is hypognathous, the eyes are lateral and the antennae are shorter than twice the width of the head. All tarsal claws are similar. In B.C. species, the rear corners of the abdominal segments project noticeably. Segments 1 to 7 bear abdominal gills, which are not forked, but may be doubled; they never end in a slender process.
Both genera in B.C., Parameletus and Siphlonurus, live across northern North America and Eurasia. Usually they develop in quiet waters – ponds or stagnant forest pools, still edges of streams – where aquatic vegetation is prevalent. Parameletus especially likes places where sedges (Carex) are abundant. Adults of this genus are usually brown. The male’s forelegs are as long as the body and the front tibiae and the first segment of the tarsi are covered with short, blunt spines. Larvae have broad, heart-shaped, single gills. P. columbiae McDunnough is the sole species reported in B.C. Siphlonurus adults are brown or purple-brown, frequently banded and spotted with paler colours, and the abdomen often has a ringed appearance. Larvae have gills double on segments 1 and 2 or on all 7 segments. They eat animals as well as plant material, often capturing bottom dwelling insects and crustacea, but especially chironomid and mosquito larvae. In Canada, the three B.C. species, S. occidentalis Eaton, S. columbianus McDunnough and S. autumnalis McDunnough are restricted to the western mountains; the first is known from the Coast range, the other two from the interior of the province.
The Heptageniidae are most diverse in northern regions of Eurasia and North America, but also occur in Africa and southeastern Asia. There are about 380 species worldwide. In North America, 14 genera contain 126 species. Eight of these genera and 23 species are known in B.C., making the family the largest in the province. Apparently there are few, if any, transcontinental species in the family, despite their close ties to rapid, cool streams – abundant habitats across the boreal forests of North America. Thus, B.C. species are largely those restricted to streams in, and west of, the Rocky Mountains.
Adult heptageniids are small to moderate in size (5 to 15 mm long without the caudal lamellae, of which there are two) and the wings are usually clear, with rather dense venation. The forewings have two pairs of cubital intercalary veins; MP1 and MP2 fork symmetrically. The eyes of adult males are simple. The hind tarsi have five segments.
The larval body is more or less flattened; the head is prognathous, usually broad and the eyes and antennae lie dorsally. Abdominal segments 1 to 7 bear single, oval (rarely slender) gills, usually bearing small, finger-like tufts near the base. There are two or three caudal appendages.
These mayflies mainly live in streams of various sorts; some inhabit lakeshores affected by strong waves, and a few kinds live in still waters. B.C. genera live in streams with fast or moderate flows. The larvae cling to the surface of stones, wood and bark and feed on algae and other organic material on the substrate surface. Some genera not occurring in B.C., notably Anepeorus and Pseudiron, are predators of small invertebrates such as the larvae of chironomid midges.
Epeorus and the related Ironodes have only two caudal filaments as larvae; the other genera known from B.C. all have three. Epeorus often has the gills expanded to form a ventral attachment disc; Ironodes does not have this feature, but has paired tubercles on the abdominal segments. There are seven species of Epeorus reported in B.C., but only one of Ironodes. I. flavipennis Traver was originally described from Okanagan Valley specimens, and apparently it is still known only from B.C. Rhithrogena (four species recorded in B.C.) also has the first and last pairs of gills meeting beneath the body to form a disc for attaching the larva to stones in rapids and riffles. The larvae of Cinygma often live on submerged wood in fast water; their gills are not expanded beneath the body and the gills on segment 1 are half the size of the others. The three named North American species are all western; C. integrum Eaton lives in B.C. Cinygmula species are common under rocks in B.C. creeks – there are six species recorded; the wings are often tinged with grey or yellow. The two species of Heptagenia recorded in the province, H. elegantula (Eaton) and H. solitaria McDunnough, are known only from the southern Interior, as is the closely related Nixe simplicicoides (McDunnough), a pale yellow, clear-winged species. Stenonema is a common genus in eastern North America, but only one or two are known from the West. The last pair of gills on the larval abdomen are reduced to slender spine-like filaments. The only Stenonema reported from B.C., S. terminatum.(Walsh), is a red-brown and pale species with clear wings; it ranges to the eastern U.S.