Key to the Orders of Insects

Notes:-
Tarsi (singular tarsus) are the last major unit of an insects leg see Fig 5.
Cerci. (singular: cercus) are the paired appendages, often very long, which project from the tip of the abdomen in many insects.
Cornicles are the pair of small tubular outgrowths which occur on the hind end of the abdomen of an aphid they, tend to point upwards and backwards from a little way forwards or the tip of the abdomen .

 

1a. Insect with wings...............................................................................................2

1b. Insect without wings........................................................................................27

2a. Insects with four wings (two pairs).....................................................................3

2b. Insects with only two wings (one pair)..............................................................25

3a. Wings covered with scales............................Butterflies and Moths Lepidoptera

3b. Wings not covered with scales, though they may be hairy..................................4

4a. Fore-wings partly or entirely horny or leathery and used as covers for

hind-wings often much narrower than hindwings............................................5

4b. Both pairs of wings entirley membranous (flexible) and used for flying...............12

5a. Mouth-parts tube-like, adapted for piercing and sucking.. True Bugs Hemiptera

5b. Mouth-parts adapted for biting and chewing.....................................................6

6a. Fore-wings and hind-wings with veins, hind-wings stiffer and harder than

and serving as covers for hind-wings..............................................................7

6b. Fore-wings without veins, and modified into hard, horny cases for hind-wings...10

7a. Body dorsoventrally flattened....................Cockroaches Dictyoptera; Blattodea

7b. Body rounded or quadrate in section..................................................................8

8a. Forelegs raptorial, adapted for grasping and holding..................Preying Mantids

...............................................................................Dictyoptera; Mantodea

8b. Forelegs not raptorial.........................................................................................9

9a. Prothorax as large as or larger than meso and meta thorax, hind legs generally

enlarged and adapted for jumping........Grasshoppers and Crickets Orthoptera

9b.Prothorax smaller than meso and meta thorax, legs normally similar in thickness,

if hind legs enlarged then not used for jumping.............Stick-Insects Phasmida

10a. Fore-wings short.............................................................................................11

10b.Fore-wings as long as, or nearly as long as abdomen the 2 wings may be joined

where they meet along the animals back and hence never used for flying..Beetles

.....................................................................................................Coleoptera

11a. End of abdomen with characteristic pair of forceps like cerci...................Earwigs

...................................................................................................Dermaptera

11b. End of abdomen with out characteristic forceps like cerci........................Beetles

.............................................................................Coleoptera; Staphylinidae

12a. Wings narrow and without veins, but fringed with long hairs. Very small insects,

about 5 mm in length ........................................................Thrips Thysanoptera

12b. Wings more fully developed, and with veins present........................................13

13a. Hind-wings noticeably smaller than fore-wings.................................................14

13b. Hind-wings similar in size to or larger than fore-wings.......................................19

14a. Abdomen with two or three long 'tails'. Fore-wings with a large number of

cross-veins, making a net-like pattern......................... Mayflies Ephemeroptera

14b. Fore-wings with fewer veins, not forming a net-like pattern,

usually without 'tails' .......................................................................................15

15a. Wings obviously hairy. Mouth-parts very small, except forpalpi

.....................................................................................Caddisflies Trichoptera

15b. Wings not obviously hairy, though tiny hairs can be seen under the microscope.....16

16a. Mouth-parts well developed and adapted for biting and chewing........................17

16b. Mouth-parts tube-like, adapted for piercing and sucking.........Aphids; Cicadas etc

....................................................................................Hemiptera; Homoptera

17a. Very small insects, soft-bodied, mostly less than 6 mm. in length. tarsi with only

two or three segments....................................................................................18

17b. Often much bigger, wasp-like or bee-like insects; or if very small, then

hard-bodied, with abdomen narrowed at its base into a petiole, or 'waist'. tarsi

with four or five segments.......... Bees, Wasps, Ants and Sawflies Hymenoptera

18a. Antennae with 9 segments only...................................................... rareZoraptera

18b. Antennae with 12 to 50 segments..........................Bark or Book Lice Psocoptera

19a. Tarsi with three or four segments only ...............................................................20

19b. Tarsi with five segments....................................................................................23

20a. Tarsi with 3 segments only; first segment of anterior (front) legs greatly swollen

................................................................................Webspinners Embioptera

20b. Tarsi with 3 or 4 segments, if 3 then first segment of anterior legs not swollen....21

21a.Wings with few cross-veins, fore-wings differently shaped to hind-wings which

are greatly expanded posteriorly......................................Stoneflies Plecoptera

21b.Wings with numerous cross veins, fore- and hind-wings usually very similar in

shape,though hind-wings occasionally enlarged posteriorly..............................22

22a. Small insects, generally much less than 1 inch. (25 mm.) in length with long

antennae, and with wings folded flat over body..................... Termites Isoptera

22b. Generally longer than 1 inch., with very short antennae. Wings held away

from body when at rest.................................................... Dragonflies Odonata

23a. Mouth-parts prolonged into a beak. ............................Scorpionflies Mecoptera

23b. Mouth-parts short...........................................................................................24

24a. Most of the veins in forewings divide or fork just before they reach the wing edge,

hind-wings broader than fore-wings at least at base ...........Alderflies, Snakeflies

..................................................................................................Megaloptera

24b. Few or no veins in the forewings fork immediatley before the wing edge,

hind-wings similar to fore-wings....................................Lacewings Neuroptera

25a. Hind-wings absent or reduced knob-like organs (called halteres)......................26

25b. Forewings absent or reduced to knob-like organ.................Stylops Strepsiptera

26a. Hind-wings reduced or modified to knob-like organs (called halteres) Mouth-parts

of various forms ..... .............................................................True Flies Diptera

(Also males of Homoptera, family Coccidae, but these are very rare)

26b. Hind-wings entirely absent; no halteres. ..............Some Mayflies Ephemeroptera

27a. Some segments with jointed legs, which can be used for movement..................28

27b. No jointed legs; or if these are present and visible, then they are enclosed

in membrane, and cannot move...................Larvae and Pupae of Endopterygota

...................................(You will need specialised keys to get these to order)

28a. Animals found living as parasites on warm-blooded animals, or found closely

associated with them i.e. in their nests or dens................................................29

28b. Animals not found living as parasites on warm-blooded animals: either freeliving,

or parasitic on other insects, snails etc............................................................34

29a. Body flattened from side to side, hard and bristly, with strong legs, jumping insects,

found on birds and mammals...............................................Fleas Siphonaptera

29b. Insects not as above, body either rounded or flattened from above ..................30

.

30a. Mouth-parts adapted for biting and or chewing.................................................31

30b. Mouth-parts adapted for piercing and or sucking..............................................32

31a. Posterior end of the body with cerci. Found on bats and small rodents in tropical

environments only.............................................. Parasitic earwigs Dermaptera

31b. Posterior end of body without cerci. On birds or mammals all over the world

................................................................................Chewing lice Mallophaga

32a. Flattened, rather spider-like insects, with head fitting into a notch on thorax, and

with antennae not visible. Claws hooked.............Louseflies and Batflies Diptera

32b. Not spider-like. Antennae clearly visible .........................................................33

33a. Snout (proboscis) short, unjointed. Body long and narrow. Tarsi of legs with one

large, hooked claw. Permanent parasites of birds and mammals......Sucking lice

........................................................................................................Anoplura

33b. Snout (proboscis) longer, jointed. Body more oval. tarsi with two small claws, not

hook-like. Only temporary parasites.........................Wingless bugs Hemiptera

34a. Terrestrial: living on dry land, or on animals other than mammals and birds........35

34b. Aquatic: mostly nymphal forms of terrestrial insects..........................................60

35a. Mouth-parts not visible. Abdomen with appendages on some of the abdominal

segments, or with a forked 'spring' near tip....................................................36

35b. Mouth-parts clearly visible..............................................................................39

36a. Abdomen with six segments or fewer, usually with a forked appendage ('spring')

near tip. No long bristles at tip of abdomen................... Springtails Collembola

36b. Abdomen with nine or more segments. No spring, but several segments have

simple appendages.......................................................................................37

37a. Cerci present, sometimes appearing as clasping forceps..................................38

37b. No cerci................................................................................................Protura

38a. A central 'cerciform tergum' projects between the cerci giving the appearance

of 3 'tails' ......................................................3-Pronged Bristletails Thysanura

38b. No central 'cerciform tergum', hence having the appearance of 2 'tails'.....

..........................................................................2-Pronged Bristletails Diplura

39a. Mouthparts mostly adapted for piercing or sucking..........................................40

39b. Mouth-parts not as above, adapted for biting and or chewing..........................44

40a. Body covered with scales and or dense hairs........ Wingless Moths Lepidoptera

40b. Body bare, or with few scattered hairs ...........................................................41

41a. Almost all of thorax that is visible above is composed of the middle segment, the

mesothorax: prothorax and metathorax both small and hidden.............................

...............................................................................Wingless True flies Diptera

41b. Mesothorax and metathorax about equally developed. Prothorax also

is usually visible from above...........................................................................42

42a. Snout (proboscis) small, cone-shaped. Body long and narrow. Claws usually

absent.............................................................................Thrips Thysanoptera

42b. Snout (proboscis) longer, jointed. Body more or less oval. Claws present.........43

43a. Proboscis arising from front part of head. Abdomen without cornicles near tip

...............................................................................Wingless Bugs Hemiptera

43b. Proboscis arising from hind part of head. Abdomen often with two cornicles

at or near its tip .............................................Aphids Hemiptera; Homoptera

44a. Abdomen with false or pro-legs, which are fleshy, and different from the

jointed legs of the thorax. Caterpillar-like......................................................45

44b. Abdomen without any kind of legs, only thorax has legs...................................47

45a. Five pairs of prolegs, or fewer, with minute hooks (crochets); none on the1st or

2nd abdominal segments...........................................Caterpillars Lepidoptera

45b. Six to ten pairs of prolegs, always with one pair on the 2nd abdominal segment.

No crochets present...............................................................................................46

46a. Head with a single ocellus (small eye) on each side.............. Larvae of Sawflies

................................................................................Hymenoptera; Symphyta

46b. Head with several ocelli on each side................. Larvae of Scorpionflies

.....................................................................................................Mecoptera

47a. Antennae short and indistinct. Larvae..............................................................48

47b. Antennae long and distinct. Adult insects.........................................................50

48a. Body Caterpillar-like.......................................................................................49

48b. Body not caterpillar-like........................... Larvae of some endopterygote insects

..............................................................................Neuroptera or Coleoptera

49a. Head with six ocelli on each side of headsome ..............Caterpillars Lepidoptera

49b. Head with more than six ocelli on each side..............Larvae of some Mecoptera

50a. Abdomen with a pair of movable forceps like cerci at tip...................Earwigs

.....................................................................................................Dermaptera

50b. Abdomen without such forceps........................................................................51

51a. Abdomen strongly constricted at base into a 'waist'. Sometimes antennae are

bent into an elbow...............................Ants and wingless Wasps Hymenoptera

51b. Abdomen not constricted into a waist...............................................................52

52a. Head prolonged underneath body into a long beak, which bears mandibles at its

tip.... ..........................................................................Scorpionflies Mecoptera

52b. Head not prolonged into a beak........................................................................53

53a. Tiny soft insects ................................................................................................54

53b. Fairly small, to very big, usually hard-bodied insect............................................55

54a. Cerci absent................................................... Booklice and Barklice Psocoptera

54b. Cerci present.......................................................................................Zoraptera

55a. Hind-legs enlarged for jumping..................................... Grasshoppers/Crickets

.......................................................................................Saltatoria; Orthoptera

55b. Hind-legs not enlarged for jumping ...................................................................56

56a. Tarsi of legs with four segments. Pale, soft-bodied insects living in wood or soil.

..............................................................................................Termites Isoptera

56b. Tarsi of legs with five segments. More highly coloured insects............................57

57a.Body dorsoventrally flattened.....................Cockroaches Dictyoptera; Blattodae

57b. Body not dorsoventrally flattened rounded or squarish in section........................58

Cerci long, containing 8 segments, eyes reduced or absent ................ Grylloblattodae

Cerci not as above, eyes well developed...................................................................59

59a. Fore-legs modified for grasping and holding, predatory....Dictyoptera; Mantodae

59b. Fore-legs not so modified................................................Stick Insects Phasmida

60a. Mouth-parts adapted for piercing and sucking. ................Nymphs of Water-bugs

.....................................................Hemiptera and larvae of some Neuroptera

60b. Mouth-parts adapted for licking and chewing.....................................................61

61a. Body enclosed in a case made of pebbles, sand and debris....Larvae of Caddisflies

......................................................................................................Trichoptera

61b. Body not enclosed in such a case......................................................................62

62a. Abdomen with external gills...............................................................................63

62b. Abdomen without external gills..........................................................................64

63a. With two or three long processes at tip of abdomen, traces of wing-cases may be

visible in later instars............................... nymphs of Mayflies Ephemeroptera

63b. Only one process at tip of abdomen, and no wing-cases visible.............Alderflies

................................................................................Megaloptera; Sialioidea

64a. Head with a 'mask', bearing the jaws which is capable of being extended far

forwards of the insect's body..........................Nymphs of Dragonflies Odonata

64b. Head without such a mask..............................................................................65

65a. With long antennae; and long filaments at tip of abdomen.....Larvae of Stoneflies

.......................................................................................................Plecoptera

65b. Without such filaments...........................................Larvae of Beetles Coleoptera