Identification Key to the Orders of Saskatchewan
Aquatic Insect Larvae and Adults

This is a typical dichotomous key used for taxonomic identifications. Each pair of numbered statements or "couplets" compares structures of the insect. By choosing the statement that best describes the character in question the reader is directed to the next assigned couplet until a name is reached. Clicking on the underlined number at the end of a couplet will automatically bring the couplet of choice to the top of the browser window. Clicking on underlined blue italics words will provide images illustrating the character in question. This key should identify to order all the larval and adult aquatic insects found in Saskatchewan.

A downloadable pdf version of this Key to the Orders of Saskatchewan Aquatic Insect Larvae and Adults is available here (1.5 meg).

More detailed family and generic keys can be found in the order links or the references listed at the bottom of the page. The key has been modified from various sources including the references at the bottom.

If you are unfamiliar with the general parts of an insect click HERE to view an image of a labelled stonefly larva. Other terms used are "dorsal" which refers to the back and "ventral" refers to the underside of the insect.

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1a: Functional wings absent or exist as small "buds or pads" on the thorax.--Go to 2

1b: Wings present and well developed (adults-there are some cases where the wings of the adult forms are reduced or absent).--Go to 17

2a: Mature insects are tiny (1-2 mm long). Most have a forked abdominal appendage which acts as a spring. They look like pepper or fleas jumping on the water surface. They are found in all quiet waters even very temporary habitats such as water filled ruts.--Collembola (Springtails)

2b: Insect larger and without forked appendage.--3

3a: Wing buds present as small flaps on top of thorax. In very immature specimens these may not be obvious--4

3b: External wing buds absent from thorax.--7

4a: Mouthparts of insect a segmented beak that may be long and thin or triangular. (Figure A shows larvae of Corixidae and Notonectidae. Arrows indicate wing buds. Figure B and C show respective beaks.).--Hemiptera (True Bugs)

4b: Mouthparts not as above.--5

5a: Mouthparts are in the form of an elbowed mask terminating in a pincer-like structure. (Arrow in figure indicates elbow of extended mask.) The mask may cover the lower portion of the face of the insect. When not extended the mask is folded between the legs at the elbow.--Odonata (Damselflies and Dragonflies)

5b: Mouthparts not in the form of an elbowed mask.--6

6a: Single claws on second and third pairs of legs. Lateral gills of various shapes present on some or all abdominal segments. (Figure shows various types of mayfly gills. A- feathery. B- pointed plate-like. C- First gill modified into a hard protective plate. D- Simple plate which may be accompanied by a frilly section.) --Ephemeroptera (Mayflies)

6b: Two claws present on all three pairs of legs. Lateral gills on abdominal segments absent although some species have ventral filamentous gills on the first two or three abdominal segments. (Figure A shows thoracic gills as well as gills on first two abdominal segments. Figure B has only thoracic gills.) Thoracic gills present or absent.--Plecoptera (Stoneflies)

7a: Specimens appear to be worm-, maggot- or caterpillar-like. True thoracic legs or false legs or prolegs may be present or absent (Prolegs are indicated by arrows.). An obvious head may be present or absent.--8

7b: Specimens have legs, antennae, and wing buds closely held to the body and maybe encased in a thin "skin" that may be transparent.--Pupae (Note in Figure A the wing and leg buds are free (Caddisfly) as compared to the other two figures (True Flies). In some groups the pupa is in a case created by the final larval instar.--(not keyed further).

8a: Three pairs of jointed legs on the thorax. In some cases the joints may be difficult to see.--9

8b: No true legs present. False legs or prolegs on the thorax and/or abdomen may be present. (Arrows indicate various types of false and prolegs.)--14

9a: Body caterpillar-like. (Figure A is of ventral surface showing crochets (circle of hooklets)). Thorax with short jointed "true" legs and the ventral surface of the abdomen with short false legs that have a circle of hooklets. The abdomen may have lateral appendages or not. The larvae may be in a case of vegetation.-- .Lepidoptera (Moths)

9b:Abdomen without circles of hooklets.--10

10a: Larvae less than 1 cm long. The mouthparts in the form of a needle. (Arrow indicates needle-like mouthparts.). Found in association with freshwater sponges.--Neuroptera (Spongilla Flies)

10b: Larvae without mouthparts as above.--11

11a: Abdomen with seven pairs of jointed lateral filaments and a single filament on the end of the abdomen. (The arrows indicate the terminal filament and some of the lateral filaments.)--Megaloptera (Alderflies)

11b: Abdomen without terminal filament. Lateral filaments if present are unjointed.(Note: The Coleoptera family Haliplidae has a terminal filament but lacks lateral filaments.)--12

12a: Abdomen with lateral filaments. End of abdomen with 4 curved claws and paired filaments.--Coleoptera- (Family Gyrinidae)

12b: Abdomen usually without lateral filaments. If lateral filaments present they are not jointed. Gill tufts may be present on the abdomen. Claws at the end of the abdomen absent or with only one pair.--13

13a: Hooked claws on short false legs present at the end of the abdomen. The larvae often construct cases out of sand or pieces of vegetation. Lateral gills present as tufts or as short single filaments.--Trichoptera (Caddisflies)

13b: Case absent. Hooked prolegs never present at the end of the abdomen.--Coleoptera (Beetles)

14a: Small, less than 2 mm, white grub. Head and legs absent. Found in the bodies or eggs of other insects.--Hymenoptera (Parasitic Wasps)

14b: Larvae not headless or legless. Vast majority are free living (i.e. not parasitic).--15

15a: Without a distinct head.--Diptera (True Flies)

15b: Larvae with a distinct head although sometimes the head may be withdrawn into the body.--16

16a: Body with no complex breathing or anchoring apparatus at posterior end.--Coleoptera (Beetles)

16b: Body with some form of breathing apparatus evident on the posterior end. (Arrows indicate breathing structures.)--Diptera (True Flies)

Adult Insects

17a: Two pairs of wings. In some groups these are modified into leathery or hard shells covering the hind pair of wings.--19

17b: Only one pair of wings. The hind pair are reduced to small balancing structures (Arrow indicates balancing organ (haltere).) or are absent.--18

18a: Hind wings reduced to small balancing structures. Abdomen without long cerci (tails).--Diptera (True Flies).

18b: Hind wings absent or extremely small relative to the forewings. Abdomen with long cerci. (Arrow indicates cerci on abdomen.).--Ephemeroptera (Mayflies).

19a: Front wings membranous with veins running through them. Venation may be covered with hairs or scales.--20

19b: Front wings hard or leathery with veins absent or only visible in the basal half.--27

20a: First abdominal segment is constricted into a thin "waist". Wing venation reduced.--Hymenoptera (Parasitic Wasps)

20b:Abdomen not constricted. Wing venation variable.--.21

21a: Wings with numerous scales that cover the wings and rub off easily. The mouth parts are in the form of a coil.--Lepidoptera (Moths)

21b: Wings without scales or coiled mouthparts.--22

22a: Legs with three tarsal segments.--23

22b: Legs with 4 or 5 tarsal segments.--24

23a: Antennae long and many segmented. Hind wing usually with an enlarged fan-like area. Cerci present at end of abdomen but sometimes only one segmented.--Plecoptera (Stoneflies).

23b: Antennae short. (Figure A: Suborder Zygoptera. Figure B: Suborder Anisoptera.). Hind wing not as above and cerci tiny.--Odonata (Damselflies and Dragonflies)

24a: Wings triangular in shape. (This image is of a subadult so the structures of the wing are more visible.) Hind wings reduced relative to fore wings. Abdomen with long cerci present. Antennae short.--Ephemeroptera (Mayflies)

24b: Hind wings about the same size as fore wings. Antennae long.--25

25a: Front region of fore wing with few crossveins. Fore wing often with numerous hairs which, unlike moths, do not rub off easily. The mouthparts are not a sucking tube.--Trichoptera (Caddisflies)

25b: Front of forewing with numerous crossveins in it.--26

26a: Adults are small and grey or brown about 1 cm long. The fore and hind wings are similar in shape. The larvae are associated with freshwater sponges so the adults will likely be in the vicinity.--Neuroptera (Spongilla Flies)

26b: Adults are larger. Hind wing broader at the base than fore wings. "Anal region" of the wings folded fan-like. Wing veins thick.--Megaloptera (Alderflies)

27a: Fore wings hard and shell-like covering the hind wings. Veins absent in fore wings.--Coleoptera (Beetles)

27b:Fore wings leathery (Arrows show leathery forewing (hemelytra) with the membranous hind wings underneath.). Mouthparts in the form of a segmented beak (Arrows indicate beaks.).--Hemiptera (True Bugs)

References:

Clifford, H.F. 1991. Aquatic Invertebrates of Alberta. University of Alberta Press. Edmonton, Alberta.

Merritt, R.W., K.W.Cummins and MB Berg. 2008. An Introduction to the Aquatic Insects of North America. Kendall/Hunt Publishing Co.. Dubuque, Iowa.