Mayfly Species Epeorus fragilis

Genitalia of the longimanus type (now a synonym of Epeorus longimanus); closely allied to I. tenuis (now a synonym of Epeorus fragilis); a small pale species.

Eyes large, greyish; head parchment color. Basal segment of antenna white, remainder light brown. Ocelli with wide brown ring at base. Thoracic notum yellowish; lateral portions of pronotum and median area of mesonotum brown; subtriangular dark areas on each side of scutella of mesonota and metanota. Pronotum deeply notched posteriorly. Pleura and sternum pale yellowish. Legs dull yellowish; a conspicuous dark brown spot near middle of each femur; claws and tarsal joinings brown. Fore legs longer than body. Wings hyaline, somewhat opaque in stigmatic area. Costa and subcosta almost colorless, other veins pale amber; cross veins rather finer than longitudinals. Humeral cross vein pale; veins of hind wing paler than fore wing.

Abdominal tergites 2-7 semi-hyaline, dull yellowish, sometimes with faint brownish tinge. Posterior margins narrowly purplish brown, the dark band slanting off obliquely toward spiracular area as it nears the pleural fold, much as in I. longimanus. Sternites paler yellowish. Segments 8-10 opaque, somewhat deeper in color. Traces of pale lunate submedian marks on middle tergites. Tails pale brownish at base, paler beyond; joinings indistinctly darker. Genitalia much as in I. longimanus; apical margin of forceps base less rounded at middle, somewhat angular. Median spines of penes more sharply outcurved toward apex, lobes of penes seem more prominent, because of deeper incisions between the apical and lateral portions.

Described as I. tenuis

Body length 7.5-8 mm, wing length 8 mm

A small pale species closely allied to I. fragilis (now a synonym of Epeorus fragilis); differs in slight details of genitalic structure, and in first pair of gills of nymph.

Head of male imago yellowish white; a narrow black line along margin of clypeus on each side of median carina. Thorax yellowish, somewhat parchment-colored. Posterior and lateral margins of pronotum very narrowly black; faint greyish shading on lateral areas. A narrow dark streak extends from lateral margin of pronotum down across prothorax to base of fore leg. Faint narrow darker markings above bases of middle and hind legs. Lateral areas on each side of scutella of mesonota and metanota darker brownish. Legs pale yellowish; femora often with faint pinkish tinge. An elongated black spot (not rounded) near middle of each femur; a faint black hair-line extends from this to base of leg. Tip of fore tibia smoky brown; tarsal joinings of middle and hind legs very narrowly brown. Fore tarsus only slightly longer than tibia. Wings hyaline; longitudinal veins pale yellowish white; cross veins hyaline, almost invisible, particularly in basal costal space. Faint whitish cloud in stigmatic area; cross veins in this area faint, about 12 in number.

Abdominal segments 2-6, and basal portion of 7, semi-hyaline, very pale yellowish white. Segments 8-10 and apical portion of 7 opaque; pale reddish brown dorsally, paler ventrally. Posterior margins of all tergites very narrowly deep purplish brown. Tails whitish, very faintly brownish at extreme base. Genitalia as in fig. 105.

This species is very closely allied to I. tenuis (now a synonym of Epeorus fragilis) and I. confusus (now a synonym of Epeorus pleuralis), with each of which it has probably been confused. Nymphs may be distinguished from each of the above species by the fact that the anterior lobes of the first pair of gills are very large and meet beneath the body of the nymph.

Described as I. tenuis

The nymph is structurally quite similar to I.fragilis ((now a synonym for Epeorus fragilis), I. fraudator (now a synonym of Epeorus pleuralis) and I. confusus (now a synonym of Epeorus pleuralis). No dark submedian spots on tergites, as in fraudator. Tracheae of gills rather indistinct. Anterior lobes of first pair of gills quite short, extend forward only a short distance beyond base of leg, so that they do not meet, or even approximately meet, beneath body of nymph. Ventrally, dark brown submedian spots on anterior margin of sternites 7-9; often an oblique dark streak laterally on sternite 9.

This small species seems to mature somewhat later than I. fragilis. The nymph is readily separated from that of fragilis by the structural characters of the first pair of gills. Penes of male somewhat more deeply and extensively lobed than in I. fragilis, especially on inner apical margin; apical margin of forceps base more regularly sinuate, its lateral projections almost on a level with the median one.