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A CPIE Notebook Project – Keys to Aquatic Biota of Hawai‘i Page A10

 
Key to Identification of Aquatic Insects

INSECTS ~ Subphylum Hexapoda ~ Class Insecta

The following key covers both adult and immature stages of aquatic insects; this page being a key to those insect Orders having aquatic representatives. For most species, only the immatures are truly aquatic and have gills. Adult aquatic insects are air-breathing animals and may live in (actually submerged), on (running over the water surface), or around (flying over) aquatic environments. This fact creates somewhat of a problem for the key because all kinds of insects may be collected near bodies of water (for example, wasps collecting mud), although these are not all aquatic insects. Some familiarity with "aquatic" insects—species that live in an aquatic environment during some stage of their life cycle—is thus helpful when using this key. Collecting specimens from within the water would seem to provide ample indication that the animals are aquatic. However, we have observed on several occassions in Hawaiian streams, areas recently flooded by rising water to be inhabited by forest litter animals (such as sowbugs, amphipods, earth worms) that were very much alive and active on the bottom of shallow pools. We have no idea how long these animals would survive submerged, but collecting from such an assemblage would result in much difficulty with our key.


[INSECT ORDERS]

   
95a (25) With well-developed wings and three pairs of jointed, thoracic legs. Adults [96]
95b

Wingless or with wings vestigial (present in much reduced form, not functional). Thoracic legs absent or 1, 2 or 3 pairs present, which may be jointed or may be simple protuberances (Fig.s 1 through 4). Pre-adults: nymphs, larvae, pupae; and some adults

[105]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
96a (95) Wings membranous, not hardened or leathery [97]
96b

Front wings hardened or leathery, forming a cover for membranous back wings; OR at least the basal portion not membranous

[104]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
97a (96) With only one pair of wings [98]
97b

With two pairs of wings

[100]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
98a (97) grouse-locust Pronotum (thorax cover) extended back over abdomen and pointed apically. Grasshopper-like, with enlarged hind legs. { 0.5 to 1 cm. Common on grass along streams and in wetlands. Grouse locust
~ Order Orthoptera ~ Family Tetrigidae


Figure I1. Paratettix mexicanus (Saussure)


98b

Pronotum not extending back over abdomen. Body not grasshopper-like nor with greatly enlarged hind legs

[99]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
99a (98) Abdomen with 2 or 3 thread-like or style-like caudal filaments (hair-like structures extending back from the tail end). Mouthparts vestigial (not developed). Antennae short and bristle-like. Mayflies
~ Order Ephemeroptera
99b

Abdomen lacking thread-like or style-like caudal filaments. Chewing or sucking mouthparts present. Tarsi (end segment of legs) comprised of five "sub-segments." Hind wings reduced to halteres (knob-like structures on the sides of the thorax). Flies
~ Order Diptera

[100]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
100a (97) Front wings relatively large, usually triangular; hind wings small, usually rounded; wings at rest held together above body. Abdomen with two or three thread-like caudal appendages. Delicate and soft-bodied. Mayfles
~ Order Ephemeroptera
100b

Not exactly as above. Wing pairs similar in size and shape, or hind wings the larger pair; wings may be held together above body at rest or out to the side. With two or no thread-like caudal appendages

[101]
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101a (100) Tarsi 5-segmented. Antennae conspicuous, longer than head [102]
101b

Tarsi with 4 or fewer segments. Antennae short, bristle-like, inconspicuous

[103]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
102a (101) Front wings conspicuously hairy. Antennae as long as body or longer; mandibles much reduced or absent. Caddisflies
~ Order Trichoptera
102b

Front wings not hairy or with microscopic hairs at most; antennae shorter than body; mandibles well developed. Lacewings
~ Order Neuroptera

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
103a (101) Wings at rest held together above body or outstretched, front pair similar in size and shape to hind pair, although may be narrower at base. Abdomen long and slender, with at most, short terminal appendages. Dragonflies & damselflies
~ Order Odonata
[125]
103b

Wings at rest held flat over abdomen. Cerci (long caudal appendages) present
~ Order Plectoptera [none in Hawai‘i]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
104a (96) Mouthparts haustellate (for piercing and sucking): an elongated and usually segmented beak arising from front part of head. Front wings usually thickened at base, membranous at tip, over-lapping at rest. True bugs
~ Order Hemiptera
[121]
104b

Mouthparts mandibulate (built for biting/chewing). Front wings hardened wing covers, without veins, meeting along a straight line down the back (usually not overlapping); antennae with 11 or fewer segments; hind wings narrow, usually longer than front wings, and with few veins. Beetles
~ Order Coleoptera

[131]
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Examples of aquatic insect pre-adult life forms

aquatic magot damselfly nymph
mosquito larva
caddisfly nymph

Figure 1. Psychodid (moth fly) larva.

Figure 2. Odonate (damselfly) nymph.

Figure 3. Culicid (mosquito) larva.

Figure 4. Trichopterid (caddisfly) larva.

105a (95) Body more or less insect-like with 2 or 3 pairs of segmented, thoracic legs and (usually) antennae (Figs. 2 & 4). Adults, nymphs, and some larvae [106]
105b

Body more or less grub-like (Fig.s 1 & 3), with body regions (head, thorax, abdomen) not so clearly defined. Segmented legs absent; legs may be conical protuberances. Antennae may be present or absent. Dipteran (fly) larvae
~ Order Diptera

[134]
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106a (105) Mouthparts haustellate (for piercing and sucking), arising from front part of head. { Wings present as rudimentary pads. Antennae 4 or 5 segmented. Tarsi (last segment of jointed leg) usually 3-segmented
~ Order Heteroptera
[115]
106b

Mouthparts mandibulate (pincher-like), not beak-like. { Wings present as pads or absent altogether

[107]
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107a (106) Compound eyes and wing pads absent. Larvae [108]
107b

Compound eyes and usually wing pads present (Fig. 2). Nymphs

[111]
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108a (107) Tarsi (last segment of jointed leg) with 1 claw [109]
108b

Tarsi with 2 claws

[110]
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109a (108) Abdomen with pair of hooks, usually on anal prolegs, at posterior end. Freshwater streams, living in cases. Caddisfly larvae
~ Order Trichoptera
109b

Abdomen with 4 hooks at posterior end or none. Not living in cases. Beetle larvae
~ Order Coleoptera

[131]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
110a (108) ~ Order Coleoptera [131]
110b

~ Order Neuroptera
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111a (107) Labium prehensile, folded under head at rest, much longer than head when extended. No caudal filaments, but may have three leaf-like gills at tip of abdomen (Fig. 2) OR stout spines. Dragonfly and damselfly nymphs
~ Order Odonata
[126]
111b

Labium normal. Three caudal filaments. Gills leaf-like or plate-like, located along sides of abdomen
~ Order Ephemeroptera


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