Key to the orders of insects

1a Insect with wings
(but the forewings could be partly or entirely stiffened as 'wing-covers' or 'wing-cases' and are not used for flying) 2

1b Insect without wings
(but there could be remnants of wings resembling small scales or pads) 32

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2a Insect with one pair of wings
3

2b Insect with two pairs of wings
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3a The dorsal surface of the prothorax extends backwards over the abdomen; the hind-legs enlarged and modified for jumping; insect looks grasshopper-like in general appearance Orthoptera
3b Insect different
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4a The wings are horny or leathery (stiff or rigid) and are not used for flying
5

4b The wings are membranous (flexible) and are used for flying
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5a The wings overlap at least a little in the centre-line and with obvious veins present Phasmida
5b The wings (elytra) meet in the centre-line (sometimes they are fused together) and without veins (note that the elytra may have longitudinal grooves or striae but these should not be confused with veins) Coleoptera

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6a The abdomen has one or more long terminal appendages
7

6b The abdomen is without terminal appendages
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7a The wings have only one forked vein; antennae are relatively long; small insect usually less than 5 mm long Hemiptera

7b The wings have many veins; antennae are short; larger insect Ephemeroptera
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8a The thorax has a pair of club-shaped structures (halteres) situated just in front of the wings Strepsiptera
8b The thorax has a pair of club-shaped structures (halteres) lying just behind the wings (these halteres may be hidden by body hairs and other structures) Diptera

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9a The forewings are partly or entirely horny or leathery and form stiffened covers for the membranous hindwings
10

9b Both pairs of wings are membranous (flexible) and used for flying (sometimes the wings are feather-like rather than membranous or their membranous nature may be obscured by a covering of hairs, scales or waxy powder)
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10a The mouth-parts form a tube-like 'beak' (rostrum) which is used for piercing and sucking (this rostrum is usually folded backwards under the body when not in use) Hemiptera

10b The mouth-parts have jaws (mandibles) and are designed for biting and chewing
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11a The forewings overlap at least a little in the centre-line and usually with many veins present
12

11b The forewings (elytra) meet in the centre-line and have no veins (note that the elytra may have longitudinal grooves or striae but these should not be confused with veins)
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12a The hind-legs are enlarged and modified for jumping; insect looks like a grasshopper in general appearance Orthoptera
12b The hind-legs are not modified for jumping and are usually similar in thickness to the middle-legs; insect is not grasshopper-like
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13a The prothorax is much larger than the head; cerci nearly always many-segmented and fairly prominent Dictyoptera
13b Prothorax and head are of similar size; cerci are not segmented and very short Phasmida
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14a The forewings (elytra) are long and cover all or most of the abdomen Coleoptera

14b The forewings (elytra) are short and much of the abdomen remains exposed
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15a The abdomen has a pair of terminal pincers or forceps Dermaptera
15b The abdomen has no terminal pincers Coleoptera

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16a The wings are very narrow without veins and fringed with long hairs (feather-like); tarsi are 1- or 2-segmented; small slender insect often found in flowers Thysanoptera

16b The wings broader with veins present; if wings are fringed with long hairs then tarsi are comprised of more than 2 segments (the wing veins of some insects may be much reduced and hardly visible or partly obscured by hairs, scales or waxy powder)
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17a The hindwings are clearly smaller than the forewings
18

17b Both pairs of wings are similar in size or hindwings larger than forewings
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18a Wings and much of the body covered with white waxy powder; tiny insect usually less than 2-3 mm long
19

18b Without powdery covering
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19a When at rest the wings are held flat over the body; the mouth-parts form a tube-like 'beak' (rostrum) for piercing and sucking (this rostrum is usually folded backwards under the body when not in use) Hemiptera

19b When at rest the wings are held roof-wise over the body; the mouth-parts have jaws (mandibles) and are designed for biting Neuroptera
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20a The wings are more or less covered with very small scales; the mouth-parts when present are forming a coiled proboscis or 'tongue' Lepidoptera

20b The wings are usually transparent (wings without scales but often hairy); the mouth-parts are not forming a coiled proboscis
21

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21a The forewings have many cross-veins making a network pattern; the abdomen has 2 or 3 long thread-like terminal appendages Ephemeroptera
21b The forewings show relatively few cross-veins; the abdomen is usually without or with only very short terminal appendages (cerci)
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22a The wings are noticeably covered with hairs; insect looks moth-like in general appearance Trichoptera
22b The wings are not noticeably hairy (but wings may be fringed with hairs or tiny surface hairs may be seen if wings are inspected under a microscope or strong hand-lens)
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23a The mouth-parts form a tube-like 'beak' (rostrum) for piercing and sucking (usually the rostrum is folded backwards under the body when not in use; the abdomen sometimes has tubular outgrowths or cornicles near the hind end) Hemiptera

23b The mouth-parts has jaws (mandibles) and are designed for biting and chewing
24

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24a The tarsi are 4- or 5-segmented; hard-bodied insects with the abdomen often constricted at its base into a petiole or narrow 'waist' Hymenoptera
24b The tarsi are 2- or 3-segmented; small soft-bodied insect
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25a Antennae with at least 12 segments Psocoptera
25b Antennae with only 9 segments Zoraptera
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26a The tarsi are 5-segmented
27

26b The tarsi are 3- or 4-segmented
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27a The wings are noticeably covered with hairs; insect is moth-like in general appearance Trichoptera
27b The wings are not noticeably hairy (but tiny hairs may be seen if the wings are observed under a microscope or with a strong hand-lens)
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28a The front of the head is extended downwards to form a beak-like structure with jaws (mandibles) at its tip Mecoptera
28b Insect without such a beak-like extension of the head Neuroptera
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29a The tarsi are 4-segmented Isoptera
29b The tarsi are 3-segmented
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30a The wings are noticeably hairy; the front tarsi are with the first segment greatly swollen Embioptera
30b The wings are not noticeably hairy; the front tarsi are simple
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31a The wings have many cross-veins, which makes a network pattern; wings are held away from the body at rest (either outstretched or folded vertically); the antennae are short and inconspicuous Odonata
31b The wings have relatively few cross-veins and are folded flat over the body when at rest; the antennae are long and slender (longer than the width of the head) Plecoptera
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32a Small soft-bodied insect which lives on terrestrial plants with the body encased under a protective shield ('scale') or the body is partly covered with white waxy filaments or powder Hemiptera

32b Insect different
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33a Thoracic legs are absent or enclosed in a membrane preventing any movement (Larvae and pupae of most Orders of Endopterygota)
33b Thoracic legs are present and fully functional
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34a The abdomen has false-legs or prolegs (prolegs are fleshy leg-like structures that are different from and additional to the jointed legs of the thorax); the insect looks like a caterpillar in general appearance
35

34b The abdomen has no prolegs; the insect is not caterpillar-like in appearance
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35a Abdomen with not more than 5 pairs of prolegs Larvae of Lepidoptera

35b Abdomen has at least 6 pairs of prolegs
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36a The head has a single small eye (ocellus) on each side Larvae of Hymenoptera
36b The head has several small eyes (ocelli) on each side Larvae of Mecoptera
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37a The insect lives in a terrestrial habitat or on the surface of water (not underwater)
38

37b The insect is truly aquatic (living underwater)
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38a The abdomen has cerci or other terminal appendages (but be careful not to confuse terminal hairs or bristles with cerci)
39

38b The abdomen does not have such terminal appendages (but it may have small appendages on proximal segments or a pair of tubular outgrowths or cornicles near the hind end)
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39a The abdomen has 6 or fewer segments; usually the abdomen has a forked terminal appendage (springing organ) folded under the rear end when not in use Collembola
39b The abdomen has more than 6 segments (usually 8 or more are clearly visible); the terminal appendages are of a different form
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40a The antennae are short and often inconspicuous (the same length as the head or shorter)
41

40b The antennae are long and conspicuous (usually they are much longer than the head)
42

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41a The tarsi have at least 3 segments (usually they are 5-segmented) Phasmida
41b The tarsi have fewer than 3 segments (often they are reduced to single or paired claws on the end of each leg) Larvae of Coleoptera

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42a The hind-legs are enlarged and modified for jumping; insect looks like a grasshopper in general appearance Orthoptera
42b The hind-legs are not modified for jumping; usually the hind-legs are similar in thickness to the middle-legs; insect does not look grasshopper-like
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43a The terminal appendages of the abdomen form a pair of pincers or forceps
44

43b The terminal appendages of the abdomen are different
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44a The tarsi are 3-segmented Dermaptera
44b The tarsi are 1-segmented Diplura
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45a The terminal appendages of the abdomen are long (much more than half the length of the abdomen)
46

45b The terminal appendages of the abdomen are short (less than half the length of the abdomen)
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46a The abdomen has 3 terminal appendages (these are a paired cerci and a median filament) Thysanura
46b The abdomen has only 2 terminal appendages (cerci)
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47a The tarsi are 3-segmented; the terminal appendages of the abdomen (cerci) are unsegmented Dermaptera
47b The tarsi are 1-segmented; the terminal appendages of the abdomen (cerci) are many-segmented Diplura
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48a The tarsi are usually 5-segmented (but sometimes fewer on regenerated legs of Phasmida)
49

48b The tarsi have fewer than 5 segments on all legs
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49a The front of the head is extended downwards to form a beak-like structure with jaws (mandibles) at its tip Mecoptera
49b Insect without such a beak-like extension of the head
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50a The prothorax is much larger than the head Dictyoptera
50b The prothorax and head are of similar size (the prothorax is at most only a little bit larger than the head)
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51a The cerci are 8-segmented and are moderately long Grylloblattodea
51b The cerci are unsegmented and are very short Phasmida
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52a The tarsi are usually 4-segmented Isoptera
52b The tarsi have fewer than 4 segments
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53a The tarsi are 1-segmented Diplura
53b The tarsi are 2- or 3-segmented
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54a The tarsi are 2-segmented Zoraptera
54b The tarsi are 3-segmented
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55a The front tarsi have a first segment which is greatly swollen; the cerci are 2-segmented Embioptera
55b The front tarsi are not swollen; the cerci are unsegmented Phasmida
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56a The insect lives as a parasite on a warm-blooded animal or it is closely associated with such an animal (for example it lives on the body or in the nest or den of a bird or mammal)
57

56b The insect is not parasitic on a warm-blooded animal
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57a The insect body is flattened from side to side; jumping insect Siphonaptera
57b The insect body is flattened from top to bottom
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58a The head is partly withdrawn into the thorax
59

58b The head is not withdrawn into the thorax
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59a The antennae are short and inconspicuous (they are much shorter than the head); legs with strong and distinctly hooked tarsal claws Diptera

59b The antennae are long and conspicuous (they are more than twice the length of the head); legs have small and only slightly curved tarsal claws Hemiptera

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60a At least the prothorax is distinct from the other thoracic segments; the legs have small tarsal claws; the mouth-parts have jaws (mandibles) and are designed for biting Mallophaga
60b All the thoracic segments are fused into a single unit; the legs have large tarsal claws which can close tightly against the legs; the mouth-parts form a tube-like proboscis for piercing and sucking (this proboscis is retracted within the head when not in use) Siphunculata
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61a Insect without antennae (very small soil-living insects usually less than 2 mm long) Protura
61b Antennae are present
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62a The abdomen is strongly constricted at its base into a narrow petiole or 'waist'; the antennae are often bent into an elbowed shape Hymenoptera
62b The abdomen is not constricted into a 'waist'; the antennae are more or less straight
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63a The body is covered with dense scales and flattened hairs Lepidoptera

63b The body is bare or with sparse bristle-like hairs
64

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64a The mouth-parts form a tube-like proboscis or rostrum for piercing and/or sucking (this proboscis is usually folded backwards under the head when not in use)
65

64b The mouth-parts are with jaws (mandibles) and designed for biting and/or chewing
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65a The tarsi are usually 5-segmented Diptera

65b The tarsi have fewer than 5 segments
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66a The proboscis is small and cone shaped (it is much shorter in length than the head) (small slender insect often found in flowers) Thysanoptera

66b The proboscis or rostrum is long and jointed (it is nearly always longer than the head) (abdomen sometimes with tubular outgrowths or cornicles near the hind end) Hemiptera

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67a The antennae are short and often inconspicuous (length of the antennae is at most about the same length as the head)
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67b The antennae are long and conspicuous (they are much longer than the head)
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68a The abdomen has 6 or fewer segments Collembola
68b The abdomen has more than 6 segments (usually 8 or more segments are clearly visible) (Larvae of various Orders)
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69a The head is narrower than the body; the mandibles are very long and protruding forward well in front of the head (the mandibles are clearly visible from above) Larvae of
Neuroptera
69b The head is as wide or nearly as wide as the body; the mandibles are small and not protruding in front of the head (they are not visible from above) Psocoptera
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70a The mouth-parts with a tube-like 'beak' or with long stylets and are designed for piercing and sucking
71

70b The mouth-parts have jaws (mandibles) and are designed for biting and/or chewing
72

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71a The mouth-parts form a robust tube-like 'beak' (rostrum) folded backwards under the body when not in use Hemiptera

71b The mouth-parts form a pair of long and slender stylets extending more or less straight forward in front of the head between the antennae and about as long or longer than the antennae Larvae of
Neuroptera
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72a Head has a hinged grasping organ (or 'mask') that can stick out; this organ bears large terminal claws (normally it is folded beneath the head when not in use) Nymphs of Odonata
72b No hinged grasping organ or 'mask' beneath the head
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73a The abdomen has pairs of feather-like or flat plate-like lateral appendages on some segments (gill filaments) and 3 long terminal appendages (paired cerci and a median filament) Nymphs of Ephemeroptera
73b Insects without this combination of features
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74a The abdomen is without lateral appendages but with 2 long terminal appendages (cerci); the antennae are long and slender (they are much longer than the head) Nymphs of Plecoptera
74b Insects without this combination of features
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75a The abdomen has pairs of multi-jointed feather-like lateral appendages on some segments (gill filaments) and sometimes a single terminal appendage Larvae of
Neuroptera
75b The abdomen is without lateral appendages (gill filaments) or if such appendages are present then they are always unjointed
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76a The last abdominal segment has a pair of fleshy appendages each bearing a strong claw; the middle- and hind-legs are longer than the width of the thorax; the body is often enclosed in a tubular case made from small pebbles or other debris Larvae of
Trichoptera
76b Insects without this combination of features Larvae of Coleoptera

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