Insects of Britain and Ireland: the orders

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L. Watson and M. J. Dallwitz

Conventional key

If you are serious about identification, you should use the interactive key. It is far superior, with flexible choice of characters, character notes and illustrations, error tolerance, full taxon descriptions, and taxon illustrations.

1(0).
  • Adults capable of flight ... 2
  • Adults flightless... 35

2(1).
  • Adult mouthparts of the biting type ... 3
  • Adult mouthparts suctorial... 28
  • Adult mouthparts adapted for both biting and sucking... 33

3(2).
  • with one pair of (membranous) propellant wings ... 4
  • with two pairs of (membranous) propellant wings... 14

4(3).
  • with conspicuously modified, raptorial fore-legs, associated with a characteristic ‘praying’ posture ... Mantodea
  • the fore-legs not conspicuously raptorial, the posture not ‘praying mantis-like’... 5

5(4).
  • Adult abdomen furnished with very large, paired, pincer-like appendages ... Dermaptera
  • Adult abdomen exhibiting a conspicuous ovipositor... 6
  • Adult abdomen with long terminal bristles ... Ephemeroptera
  • Adult abdomen not spectacularly appendaged... 8

6(5).
  • The adults with hardened ‘elytra’ (q.v., representing the fore-wings) ... Coleoptera
  • The adults without elytra... 7

7(6).
  • Fore-wings membranous; hind-wings smaller than the fore-wings; hind-wings no broader than the fore-wings; wings of similar texture in both pairs; development involving marked metamorphosis ... Hymenoptera
  • Fore-wings leathery; hind-wings larger than the fore-wings; hind-wings markedly broader than the fore-wings; wings markedly differently textured in the two pairs; development gradual ... Orthoptera

8(5).
  • Adult mouthparts conforming to the generalized biting type ... 9
  • Adult mouthparts highly modified... 13

9(8).
  • The adults with hardened ‘elytra’ (q.v., representing the fore-wings) ... 10
  • The adults without elytra... 11

10(9).
  • Abdomen apparently 8 to 9 segmented; abdomen lacking clearly visible cerci; the eggs not laid in batches within a protective case (ootheca); development involving marked metamorphosis; development endopterygote ... Coleoptera
  • Abdomen apparently 10 segmented or more; abdomen with cerci clearly visible at its tip; the eggs laid in batches within a protective case (ootheca); development gradual; development exopterygote ... Blattodea

11(9).
  • Head prolonged into a rigid beak ... Mecoptera
  • Head not rigidly beaked... 12

12(11).
  • Fore-wings membranous; hind-wings smaller than the fore-wings; hind-wings no broader than the fore-wings; wings of similar texture in both pairs; development involving marked metamorphosis ... Hymenoptera
  • Fore-wings leathery; hind-wings larger than the fore-wings; hind-wings markedly broader than the fore-wings; wings markedly differently textured in the two pairs; development gradual ... Orthoptera

13(8).
  • the adult males actively flying, having fore-wings reduced to knobbed, haltere-like structures and large, membranous hind-wings; females larviform and confined to puparia inside hymenopterous or hemipterous hosts ... Strepsiptera
  • the adult males not having fore-wings reduced to knobbed, haltere-like structures, and the females not larviform parasites; i.e., by contrast with Strepsiptera ... Hymenoptera

14(3).
  • Ocelli 0 ... 15
  • Ocelli 2... 19
  • Ocelli 3... 20

15(14).
  • Hind-wings smaller than the fore-wings ... 16
  • Hind-wings similar in size to the fore-wings ... Neuroptera
  • Hind-wings larger than the fore-wings... 18

16(15).
  • Wings fringed; wings conspicuously scaly ... Lepidoptera
  • Wings not fringed; wings more or less naked... 17

17(16).
  • Wings of the resting insect held roof-like over the abdomen; the clypeus divided into a narrow, transverse anteclypeus and a characteristically bulbous postclypeous; development gradual; development exopterygote; development not involving a pupal stage ... Psocoptera
  • Wings of the resting insect not held roof-like; the clypeus not transversely divided and bulbous above as in Psocoptera (q.v.); development involving marked metamorphosis; development endopterygote; development involving a pupal stage ... Hymenoptera

18(15).
  • Wings conspicuously hairy ... Neuroptera
  • Wings conspicuously scaly ... Lepidoptera
  • Wings more or less naked ... Neuroptera

19(14).
  • Wings fringed; tarsi 5 segmented; wings conspicuously scaly; development involving marked metamorphosis; abdomen lacking clearly visible cerci ... Lepidoptera
  • Wings not fringed; tarsi 3 segmented; wings more or less naked; development gradual; abdomen with cerci clearly visible at its tip ... Plecoptera

20(14).
  • Wings of the resting insect held above the body, with their upper surfaces more or less apposed ... 21
  • Wings of the resting insect outspread... 22
  • Wings of the resting insect closed and directed backwards... 23

21(20).
  • Adult mouthparts well developed; adult mouthparts functional for feeding; adults not particularly associated with water; larvae terrestrial; development involving marked metamorphosis ... Hymenoptera
  • Adult mouthparts much reduced; adult mouthparts non-functional for feeding; adults nearly always found near water; larvae aquatic; development gradual ... Ephemeroptera

22(20).
  • Hind-wings smaller than the fore-wings; adults not particularly associated with water; larvae terrestrial; development involving marked metamorphosis; development endopterygote ... Hymenoptera
  • Hind-wings similar in size to the fore-wings; adults nearly always found near water; larvae aquatic; development gradual; development exopterygote ... Odonata

23(20).
  • with the prothorax remarkably elongated, forming with the narrowed back of the head a greatly elongated ‘neck’ ... Raphidioptera
  • without the ‘neck’ characteristic of Raphidioptera... 24

24(23).
  • Wings of the resting insect held roof-like over the abdomen ... 25
  • Wings of the resting insect not held roof-like... 26

25(24).
  • Hind-wings smaller than the fore-wings ... Psocoptera
  • Hind-wings similar in size to the fore-wings ... Neuroptera
  • Hind-wings larger than the fore-wings ... Neuroptera

26(24).
  • Head prolonged into a rigid beak ... Mecoptera
  • Head not rigidly beaked... 27

27(26).
  • Hind-wings smaller than the fore-wings; hind-wings no broader than the fore-wings; adults not particularly associated with water; larvae terrestrial; development involving marked metamorphosis ... Hymenoptera
  • Hind-wings larger than the fore-wings; hind-wings markedly broader than the fore-wings; adults nearly always found near water; larvae aquatic; development gradual ... Plecoptera

28(2).
  • with one pair of (membranous) propellant wings ... 29
  • with two pairs of (membranous) propellant wings... 31

29(28).
  • Hind-wings represented by small, clubbed ‘halteres’; larvae without segmented thoracic legs; development involving marked metamorphosis; development endopterygote; development involving a pupal stage ... Diptera
  • Hind-wings not represented by halteres; larvae with three pairs of segmented thoracic legs; development gradual; development exopterygote; development not involving a pupal stage... 30

30(29).
  • Wings of the resting insect held above the body, with their upper surfaces more or less apposed; head not rigidly beaked; adult mouthparts much reduced; adult mouthparts non-functional for feeding; adult mouthparts not piercing ... Ephemeroptera
  • Wings of the resting insect closed and directed backwards; head prolonged into a rigid beak; adult mouthparts well developed; adult mouthparts functional for feeding; adult mouthparts piercing ... Hemiptera

31(28).
  • Wings exhibiting ‘corneous dots’ ... Trichoptera
  • Wings without ‘corneous dots’... 32

32(31).
  • Ocelli 0 ... Lepidoptera
  • Ocelli 2 ... Lepidoptera
  • Ocelli 3 ... Ephemeroptera

33(2).
  • Adult mouthparts piercing ... Thysanoptera
  • Adult mouthparts not piercing... 34

34(33).
  • Adult mouthparts well developed; adult mouthparts functional for feeding; adults not particularly associated with water; development involving marked metamorphosis; larvae terrestrial ... Hymenoptera
  • Adult mouthparts much reduced; adult mouthparts non-functional for feeding; adults nearly always found near water; development gradual; larvae aquatic ... Ephemeroptera

35(1).
  • Adult mouthparts of the biting type ... 36
  • Adult mouthparts suctorial... 59
  • Adult mouthparts adapted for both biting and sucking... 63

36(35).
  • Abdomen exhibiting rudimentary abdominal limbs ... 37
  • Abdomen with no rudimentary abdominal limbs... 39

37(36).
  • Ocelli 0 ... 38
  • Ocelli 1 ... Thysanura
  • Ocelli 2 ... Protura
  • Ocelli 3 ... Archaeognatha

38(37).
  • Tarsi 1 segmented ... Diplura
  • Tarsi 2 segmented ... Thysanura
  • Tarsi 3 segmented ... Thysanura
  • Tarsi 4 segmented ... Thysanura
  • Tarsi 5 segmented ... Thysanura

39(36).
  • with conspicuously modified, raptorial fore-legs, associated with a characteristic ‘praying’ posture; the eggs laid in batches within a protective case (ootheca) ... Mantodea
  • the fore-legs not conspicuously raptorial, the posture not ‘praying mantis-like’; the eggs not laid in batches within a protective case (ootheca)... 40

40(39).
  • Head prognathous ... 41
  • Head hypognathous... 45

41(40).
  • Adult mouthparts conforming to the generalized biting type ... 42
  • Adult mouthparts highly modified... 44

42(41).
  • slender and remarkably stick-like in appearance (‘stick insects’); abdomen with cerci clearly visible at its tip ... Phasmatodea
  • not slender and stick-like in appearance (not ‘stick insects’); abdomen lacking clearly visible cerci... 43

43(42).
  • The adults highly specialized, very dorsoventrally flattened, blind external parasites, which spend their whole lives clinging to their hosts via their modified tarsi; the adults without elytra; development gradual; development apterygote; development not involving a pupal stage ... Phthiraptera
  • The adults not having the peculiar features of Pthiraptera; the adults with hardened ‘elytra’ (q.v., representing the fore-wings); development involving marked metamorphosis; development endopterygote; development involving a pupal stage ... Coleoptera

44(41).
  • Compound eyes present and well developed; the adults not having the peculiar features of Pthiraptera; the adult males actively flying, having fore-wings reduced to knobbed, haltere-like structures and large, membranous hind-wings; females larviform and confined to puparia inside hymenopterous or hemipterous hosts; larvae without segmented thoracic legs; development involving marked metamorphosis ... Strepsiptera
  • Compound eyes vestigial or absent; the adults highly specialized, very dorsoventrally flattened, blind external parasites, which spend their whole lives clinging to their hosts via their modified tarsi; the adult males not having fore-wings reduced to knobbed, haltere-like structures, and the females not larviform parasites; i.e., by contrast with Strepsiptera; larvae with three pairs of segmented thoracic legs; development gradual ... Phthiraptera

45(40).
  • Ocelli 0 ... 46
  • Ocelli 1 ... Coleoptera
  • Ocelli 2... 53
  • Ocelli 3... 55

46(45).
  • The wingless adults not larva-like, with only obscure thoracic segmentation ... 47
  • The wingless adults larva-like, with the thorax clearly segmented... 51

47(46).
  • Body and legs of wingless adults bearing scales ... Lepidoptera
  • Body and legs of wingless adults without scales... 48

48(47).
  • The clypeus divided into a narrow, transverse anteclypeus and a characteristically bulbous postclypeous ... 49
  • The clypeus not transversely divided and bulbous above as in Psocoptera (q.v.)... 50

49(48).
  • Abdomen apparently 8 to 9 segmented; abdomen lacking clearly visible cerci ... Psocoptera
  • Abdomen apparently 10 segmented or more; abdomen with cerci clearly visible at its tip ... Orthoptera

50(48).
  • Development gradual; development exopterygote; development not involving a pupal stage ... Orthoptera
  • Development involving marked metamorphosis; development endopterygote; development involving a pupal stage ... Hymenoptera

51(46).
  • Adult mouthparts conforming to the generalized biting type; the adult males not having fore-wings reduced to knobbed, haltere-like structures, and the females not larviform parasites; i.e., by contrast with Strepsiptera ... 52
  • Adult mouthparts highly modified; the adult males actively flying, having fore-wings reduced to knobbed, haltere-like structures and large, membranous hind-wings; females larviform and confined to puparia inside hymenopterous or hemipterous hosts ... Strepsiptera

52(51).
  • The adults with hardened ‘elytra’ (q.v., representing the fore-wings); abdomen apparently 8 to 9 segmented; abdomen lacking clearly visible cerci; development involving marked metamorphosis; development endopterygote ... Coleoptera
  • The adults without elytra; abdomen apparently 10 segmented or more; abdomen with cerci clearly visible at its tip; development gradual; development exopterygote ... Orthoptera

53(45).
  • Body and legs of wingless adults bearing scales ... Lepidoptera
  • Body and legs of wingless adults without scales... 54

54(53).
  • The adults with hardened ‘elytra’ (q.v., representing the fore-wings); abdomen apparently 8 to 9 segmented; abdomen lacking clearly visible cerci; development involving marked metamorphosis; development endopterygote ... Coleoptera
  • The adults without elytra; abdomen apparently 10 segmented or more; abdomen with cerci clearly visible at its tip; development gradual; development exopterygote ... Orthoptera

55(45).
  • Head prolonged into a rigid beak ... Mecoptera
  • Head not rigidly beaked... 56

56(55).
  • The clypeus divided into a narrow, transverse anteclypeus and a characteristically bulbous postclypeous ... 57
  • The clypeus not transversely divided and bulbous above as in Psocoptera (q.v.)... 58

57(56).
  • Abdomen apparently 8 to 9 segmented; abdomen lacking clearly visible cerci ... Psocoptera
  • Abdomen apparently 10 segmented or more; abdomen with cerci clearly visible at its tip ... Orthoptera

58(56).
  • Development gradual; development exopterygote; development not involving a pupal stage ... Orthoptera
  • Development involving marked metamorphosis; development endopterygote; development involving a pupal stage ... Hymenoptera

59(35).
  • Compound eyes present and well developed ... 60
  • Compound eyes vestigial or absent... 62

60(59).
  • Head prolonged into a rigid beak; development gradual; development exopterygote; development not involving a pupal stage ... Hemiptera
  • Head not rigidly beaked; development involving marked metamorphosis; development endopterygote; development involving a pupal stage... 61

61(60).
  • Body and legs of wingless adults bearing scales; larvae with three pairs of segmented thoracic legs; the larval abdominal prolegs bearing crochets; larval head with a well sclerotized capsule ... Lepidoptera
  • Body and legs of wingless adults without scales; larvae without segmented thoracic legs; the larval abdominal prolegs without crochets; larval head without a well sclerotized capsule ... Diptera

62(59).
  • Head prognathous; adults not ‘jumpers’; adult body dorsiventrally flattened; the adults highly specialized, very dorsoventrally flattened, blind external parasites, which spend their whole lives clinging to their hosts via their modified tarsi; larvae with three pairs of segmented thoracic legs ... Phthiraptera
  • Head hypognathous; adults conspicuous ‘jumpers’; adult body laterally flattened; the adults not having the peculiar features of Pthiraptera; larvae without segmented thoracic legs ... Siphonaptera

63(35).
  • Abdomen exhibiting rudimentary abdominal limbs; adults conspicuous ‘jumpers’; tarsi reduced to pretarsal claws terminating the tibiae ... Collembola
  • Abdomen with no rudimentary abdominal limbs; adults not ‘jumpers’; tarsi not completely reduced to pretarsal claws... 64

64(63).
  • Adult mouthparts piercing; development gradual; development exopterygote; development not involving a pupal stage ... Thysanoptera
  • Adult mouthparts not piercing; development involving marked metamorphosis; development endopterygote; development involving a pupal stage ... Hymenoptera


To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. Insects of Britain and Ireland: orders. Version: 16th May 2016. delta-intkey.com’.

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