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likely to cause trouble for the beginner are those of the gill remnants, since these structures are often shriveled in dry pinned specimens and are difficult to evaluate; they are more easily studied in specimens preserved in alcohol. Length is measured from front of head to wing tips (wings in a resting position). No. of species: World, 1550; N. America, 400.

Suborder Systellognatha

Cerci much longer than greatest width of pronotum. First tarsal segment much shorter than 3rd. Usually no forked vein rising from basal anal cell in FW. Adults appear in late spring and summer, usually nocturnal and nonfeeding.

COMMON STONEFLIES Family Perlidae Identification: Color variable but usually yellowish to brownish and not green. Mostly 15-40 mm. Remnants of branched nymphal gills on ventral side of thorax, usually immediately behind bases of legs.

This family is the largest in the order, and its members are the stoneflies most often collected. Most nymphs are predaceous. One of the largest and commonest genera is Acroneuria; some species in this genus are quite large (to 40 mm.) and resemble pteronarcids but lack the rows of cross veins in the anal area of the front wings.

adult gill remnants

Thorax (ventral) COMMON STONEFLY

GREEN-WINGED STONEFLIES Family Isoperlidae Identification: Body greenish or yellowish, wings usually greenish. 6-15 mm. No remnants of nymphal gills on thorax. Front corners of pronotum acute or narrowly rounded. Anal lobe of HW well developed, with 4 or more veins reaching wing margin, cf without a lobe on 8th sternum, and 10th tergum usually not notched. 9 subgenital plate generally small.

These are fairly common stoneflies, and adults are often seen running about on foliage near streams; many are pollen feeders. Nymphs vary in habits. This family contains a single N. American genus, Isoperla.

PERLODID STONEFLIES Family Perlodidae Identification: Similar to Isoperlidae but 10-25 mm. and brownish or blackish; wings not greenish. Either no remnants of nymphal gills on ventral side of thorax or a remnant of a fingerlike gill on each side of base of labium. d" usually with a lobe on posterior margin of 7th abdominal sternum, and 10th tergum with a deep median notch. 9 subgenital plate generally large.

Nymphs occur in medium-sized to large streams, and adults appear in the spring or early summer. Most species are northern or western, and they are not common.

GREEN STONEFLIES Family Chloroperlidae Identification: Length 6-24 (mostly 6-15) mm. Usually yellowish or greenish. No remnants of nymphal gills on ventral side of thorax. Front corners of pronotum broadly rounded. Either a forked vein rising from basal anal cell in FW or anal lobe in HW reduced (with 3 or fewer veins) or absent, cF without a lobe on either 7th or 8th abdominal sternum.

Nymphs usually occur in small streams, and adults appear in spring.

Suborder Holognatha

Cerci variable in length but usually short, no longer than greatest width of pronotum. Often a forked vein comes off basal anal cell in FW. Mandibles generally well developed. Most adults diurnal and plant feeding.

GIANT STONEFLIES Family Pteronarcidae Identification: Length in. Usually brown or gray.

Anal area of FW with 2 or more rows of cross veins.

Nymphs are plant feeders and occur in medium-sized to large rivers. Adults appear in spring and early summer. Adults are largely nocturnal and do not feed; often are attracted to lights.

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