Aquatic Insects of Michigan

by Ethan Bright, Museum of Zoology Insect Division and School of Natural Resources and Environment
University of Michigan

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Stenacron (Ephemeroptera: Heptageniidae)

Imagos (males only: adapted from Lewis 1974)

    1a Outer lateral margins of penis lobes without a cluster of large spines, although extremly minute spines may be present Stenacron candidum (Traver)
    also: Penis lobes with terminal or subterminal spines; black spiracular dots on Ab4-8 terga; black dashes on face below antennae
    1b Outer lateral margins of penis lobes with a cluster of large spines 2
    2a(1b) Lobes of penis with discal spines Stenacron interpunctatum (Say) (in part)
    also: no axial spine on penis lobe; apical spine of each penis lobe, if present, smaller than discal spine; either with a black streak present on pleuron ventral to fore wing base, a black dash connecting cross veins below bulla in fore wing, or with spiracular dots present
    2b Lobes of penis with terminal or subterminal spines 3
    3a(2a) In ventral view, abdomen with a median, longitudinal dark line extending from anterior to posterior ends, this line slightly widened and with a narrow interruption at the posterior margin of each sternum Stenacron gildersleevei (Traver)
    3b Abdomen not as above, in ventral view usually entirely pale or faint dark marks at the posterior margin of some sterna Stenacron interpunctatum (Say) (in part)

Mature nymphs (adapted from Lewis 1974)

    1a a. Each maxilla with 30 or more lateral setae Stenacron gildersleevei (Traver)
    b. Crown of maxilla with 11-13 heavy pectinate spines
    also: sterna 7-9 without dark bands or spots
    1b a. Each maxilla with less than 30 lateral setae 2
    b. Crown of maxilla with 7-10 spines
    2a(1b) Inner margin of outer canine of left mandible with 8 teeth Stenacron candidum (Traver)
    2b Inner margin of outer canine with 5-7 teeth Stenacron interpunctatum (Say)
    also: In dorsal view, pale longitudinal streaks the length of the abdomen continuous or nearly so, usually some distinct dark markings on posterior sterna; very common, widely distributed


    Lewis PA. 1974. Taxonomy and ecology of Stenonema(it.) mayflies (Heptageniidae: Ephemeroptera). National Environmental Research Center, U.S. Environmental Protection Agency, Cincinnati, Ohio. EPA-670/4-74-006. 89 p.

Page created: November 10, 2003; Last edited: November 06, 2013 (EB)