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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Orders of Aquatic and Semiaquatic Insects

Below is a provisional key for insects that one generally encounters in freshwater aquatic and semiaquatic environments (from Daly 1996). Sometimes during sampling terrestrial organisms are taken, and may not key correctly here. In this case the reader is referred to the work by Borrer et al. 1989.

    1a a. Wings or wing pads present, fore wings sometimes hard and shell-like, concealing hind wings
    b. Legs present
    1b a. Wings or wing pads entirely absent 27
    b. Legs present or absent
    2a(1a) Wings fully developed, usually conspicuous and movable (adults)
    2b Wings developing in fixed wing pads (larvae and pupae) 15
    3a(2a) Forewings leathery or hard, at least in the basal half
    3b Wings entirely membranous 6
    4a(3a) Sucking mouthparts united in a jointed beak, mandibles concealed
    Heteroptera (Hemiptera), adults
    4b Chewing mouthparts, mandibles visible 5
    5a(4b) Forewings leathery, veins distinct; hind femora enlarged for jumping Orthoptera, adults
    5b Forewings sclerotized, hard (elytra), veins indistinct; hind legs not modified for jumping, but suited for walking or swimming Coleoptera, adults
    6a(3b) One pair of wings 7
    6b Two pair of wings 8
    7a(6a) a. Abdomen ending in 2-3 long filaments
    Ephemeroptera, adults
    b. Mouthparts inconspicuous
    c. Metathorax without club-shaped structure
    7b a. Abdomen without conspicuous filaments Diptera, adults
    b. Mouthparts well-developed, forming a proboscis
    c. Metathorax with club-shaped halteres
    8a(6b) Wings covered with scales or hairs, obscuring venation 9
    8b Wings bare or with only minute hairs, wing venation clearly visible 10
    9a(8a) a. Wings with scales Lepidoptera, adults
    b. Mouthparts usually fitted with a coiled sucking tube
    9b a. Wings with hairs Trichoptera, adults
    b. Mouthparts without a coiled sucking tube, rather mandibulate
    10a(8b) Antennae short, bristlelike, and inconspicuous 11
    10b Antennae of various shapes, conspicuous, not bristlelike 12
    11a(10a) a. Abdomen ending in 2-3 long filaments Ephemeroptera, adults
    b. Wings about equal in size
    11b a. Abdomen without long filaments Odonata, adults
    b. Wings about equal in size
    12a(10b) a. Tarsi 2- or 3- segmented Plecoptera, adults
    b. Abdomen ending with 2 conspicuos cerci (reduced in some adult Nemouridae)
    12b a. Tarsi 5-segmented (except 3-segmented in some Hymenoptera) 13
    b. Abdomen without conspicuous appendages
    13a(12b) a. Abdomen with narrow constriction at junction with the thorax Hymenoptera, adults
    b. Marginal veins in basal half of forewing parallel to leading edge
    c. Wings with fewer than 20 closed cells
    also: Aquatic forms very small, usually < 3 mm in length
    13b a. Abdomen broadly joined to thorax 14
    b. Front margin of forewing in basal half with many small veins perpendicular to edge
    c. Wings with more than 20 closed cells

    Hindwings folded or pleated lengthwise

    Megaloptera, adults
    14b Hindwings not folded Neuroptera (Sisyridae), adults
    15a(2b) a. Active insects with legs freely movable nymphs/larvae, 16
    b. Not in cocoons or capsule-like cases
    15b a. Usually inactive insects, "mummy-like" with appendages drawn up and free or fused to body pupae, 20
    b. Sometimes in cocoons or sealed in capsule-like cases or puparia
    16a(15a) Sucking mouthparts united in a jointed beak with mandibles concealed Heteroptera (Hemiptera), nymphs
    16b Chewing mouthparts, with mandibles distinct 17
    17a(16b) a. Hindlegs suited for jumping, hind femora greatly enlarged Orthoptera, nymphs
    b. Abdomen without long cerci
    c. Found in moint places and only temporarily in water
    17b a. Hindlegs suited for crawling, hind femora not greatly enlarged, approximately the smae size as front and middle femora 18
    b. Abdomen with or without conspicuous terminal appendages
    c. Usually submerged, truly aquatic
    18a(17b) Labium (lower lip) masklike, extendable into a graspable, often scoop-like structure longer than the head Odonata, nymphs
    18b Labium normal, smaller than head, not large and masklike 19
    19a(18b) a. Tarsi with one claw (sometimes foretarsi bifurcated, but eminate from one claw base) Ephemeroptera, nymphs
    b. Abdomen terminating with 3 (sometimes only 2) long filaments
    c. Gills and or lamellae located on sides of abdomen, may be platelike, filamentous, or feathery
    19b a. Tarsi with two clearly differentiated claws on all legs Plecoptera, nymphs
    b. Abdomen terminating only with 2 long filaments
    c. Gills absent or present, fingerlike or filamentous, located at base of mouthparts (inconspicuous), head, coxae, or on thorax or abdomen segments 1-2 (in Michigan)
    20a(15b) Appendages free, distinct, not fused to body (exarate) pupae, 21
    20b Appendages fused to body (obtect), or concealed in hardened capsule (coarctate) pupae, 26
    21a(20b) Abdomen with constriction where joined to thorax Hymenoptera, pupae
    21b Abdomen broadly joined to thorax 22
    22a(21b) One pair of wingpads Diptera, pupae
    22b Two pair of wingpads 23
    23a(22b) a. Pads of forewings thickened Coleoptera, pupae
    b. Antennae usually with 11 or fewer segments
    23b a. Pads of forewings not thickened 24
    b. Antennae 12 or more segments
    24a(23b) a. Mandibles curved, projecting forward and usually crossing each other Trichoptera, pupae
    b. Pupae usually submerged in water (maybe in damp areas of overhanging stream banks)
    also: Always in cases
    24b a. Mandibles not as above, rather stout and not crossing each other 25
    b. Pupae terrestrial (near water's edge), not normally submerged
    25a(24b) a. Smaller, body length < 10 mm Neuroptera (Sisyridae), pupae
    b. Pupae in double-walled, meshlike cocoons in sheltered places
    25b a. Larger, body length > 12 mm Megaloptera, pupae
    b. Pupae in chambers in soil or rotten wood, without cocoons
    26a(20b) a. Appendages visible on pupal surface Lepidoptera, pupae
    b. Without obvious breating tubes or gills
    c. Two pairs of wingpads present (hindwings mostly concealed beneath forewings)
    26b a. Appendages visible or entirely concealed in barrel-shpaed capsule Diptera, pupae
    b. If appendages visible, then usually with projecting respiratory organs, or paired, dorsal, prothoracic breating tubes, sometimes with gills at the abdominal tip
    c. One pair of wingpads
    27a(1b) a. Abdomen with 6 or fewer segments, with a ventral tube (collaphore) Collembola, immatures and adults
    b. Minute, body length < 5 mm
    27b a. Abdomen with more than 6 segments, without a ventral tube 28
    b. Body length longer, usually > 5 mm
    28a(27b) Three pairs of jointed legs present on thorax 29
    28b True legs absent; fleshy, leglike protuberances or prolegs may be present on thorax, but fewer than three pairs and not jointed 34
    29a(28a) a. Middle- and hindlegs long and slender, extending considerably beyond the abdomen Heteroptera (Hemiptera), nymphs and adults
    b. Compound eyes present (nymph, wingless adult Gerridae)
    29b a. Legs not longer than the abdomen 30
    b. Compound eyes absent
    30a(29b) Abdomen with at least two pairs of ventral, fleshy, leglike protuberances tipped with tiny hooks (prolegs with crochets) Lepidoptera, larvae
    30b Abdomen without leglike protuberances, or, if present, not tipped with tiny hooks 31
    31a(30b) a. Last abdominal segment with lateral appendages bearing hooks (anal hooks) Trichoptera, larvae
    b. Antennae 1-segmented, inconspicuous
    c. Gills, if present, seldom confined to lateral margins of body
    also: Larvae free-living or in cases made of stone or sand grains and/or bits of plant matter
    31b a. Last abdominal segment without anal hooks 32
    b.Or, if anal hooks present, antennae of more than 1 segment
    c. Gill insertions lateral
    32a(31b) a. Mouthparts formed with mandibles and maxillae united at each side to form long, straight or slightly recurved thread-like suctorial tubes Neuroptera (Sisyridae), larvae
    b. Laterally inserted, segmented gills folded beneath abdomen
    c. Body length small, < 10 mm
    d. Found in or on freshwater sponges
    32b a. Mounthparts with mandibles not united with maxillae, if mandibles suctorial, then strongly curved 33
    b. Gills seldom segmented and not folded beneath abdomen
    c. Body length variable
    d. Not directly associated with sponges
    33a(32b) a. Abdomen with 7 or 8 pairs of lateral filaments or gills, arranged 1 pair on each segment Megaloptera, larvae
    b. Ab9 with hooked lateral appendages (anal hooks), or a single, medial, caudal filament
    33b a. Abdomen usually without lateral gills, or, if present, then 1) anal hooks absent, or 2) Ab10 with 4 gills, or 3) caudal appendage paired or absent, never single Coleoptera, larvae
    34a(28b) Head capsule distinct, partly or entirely hardened, and usually pigmented, but may be deeply withdrawn in prothorax 35
    34b Head capsule absent, not distinct, hardened, or pigmented, often consisting of a few pale rods 36
    35a(34a) Posterior end of body with at least one or a combination of gills, hair brushes, a sucker, or breathing tube Diptera (in part), larvae
    35b Posterior end of body simple, or with small processes or isolated hairs, but without gills, brushes, suckers, or breathing tubes Coleoptera (Curculionidae), larvae
    36a(34b) a. Body usually > 5 mm, elongate, somewhat cylindrical, spindle-shaped or maggotlike Diptera (in part), larvae
    b. Mouthparts may be reduced to a pair of retractile mouth hooks that move vertically
    36b a. Body usually < 5 mm Hymenoptera, larvae
    b. Mouthparts may be reduced to a pair of opposable, acute mandibles that move horizontally; parasitoids on or inside insect hosts


    Borrer DJ, Triplehorn CA, Johnson NF. 1989. An Introduction to the Study of Insects (6th Edition). Saunders College Publications: Philadelphia, Pennsylvania. 875 p.
    Daly HV. 1996. General classification and key to the orders of aquatic and semiaquatic insects, pp. 108-112 in Merritt RW, Cummins KW, An Introduction to the Aquatic Insects of North America, 3rd Edition. Kendall/Hunt Publishing Co.: Dubuque, Iowa. xiii + 862 p.

Page created: May 19, 2003; Last edited: November 05, 2013 (EB)