Insects of Britain and Ireland: the families of Hymenoptera

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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).
  • The abdomen broadly sessile at its base, without a marked constriction (the insects not noticeably ‘waisted’: Symphyta) ... 2
  • The abdomen with a marked basal constriction (the insects ‘waisted’: Apocrita)... 14

2(1).
  • Sub-antennal grooves present (to accommodate the laterally and somewhat ventrally directed antennal scape) ... 3
  • Sub-antennal grooves absent... 5

3(2).
  • Adults conspicuously bearing a spherical head on an elongated ‘neck’ ... Xiphydriidae
  • Adults not conspicuously spherical-headed and ‘necked’... 4

4(3).
  • Antennae inserted above the lower margins of the eyes; fore-wings with a conspicuous pterostigma; hind-wings with closed cells ... Siricidae
  • Antennae inserted below the eyes; fore-wings without a pterostigma; hind-wings without closed cells ... Orussidae

5(2).
  • Antennae with a very elongated third segment ... 6
  • Antennae without noticeable elongation of the third segment... 7

6(5).
  • Antennal segments 3 ... Argidae
  • Antennal segments 4 ... Blasticotomidae
  • Antennal segments 11 to 15 ... Xyelidae
  • Antennal segments 16 to 25 ... Xyelidae

7(5).
  • Cenchri present ... 8
  • Cenchri absent... 11

8(7).
  • Pronotum more or less straight at the back ... 9
  • Pronotum deeply indented or emarginate at the back... 10

9(8).
  • The antennal flagellum serrate via distinctly produced segments ... Megalodontidae
  • The antennal flagellum simple and not serrate, the segments not produced ... Pamphiliidae

10(8).
  • Antennal segments 4 ... Cimbicidae
  • Antennal segments 5 to 7 ... Cimbicidae
  • Antennal segments 8 to 9 ... Tenthredinidae
  • Antennal segments 10 ... Tenthredinidae
  • Antennal segments 11 to 15 ... Tenthredinidae
  • Antennal segments 16 to 25 ... Diprionidae

11(7).
  • Hind femur with a clear trochantellus ... 12
  • Hind femur without a well defined trochantellus... 13

12(11).
  • Larvae with segmented legs; larvae parasitic on hosts selected by the mother ... Braconidae
  • Larvae legless or the legs vestigial; larvae phytophagous ... Cephidae

13(11).
  • Antennal segments 11 to 15 ... Heloridae
  • Antennal segments 16 to 25 ... Cephidae
  • Antennal segments 26 or more ... Cephidae

14(1).
  • The ‘waist’ with scales or nodes (including forms appearing ‘double- or several-waisted’) ... 15
  • The ‘waist’ simple (node-less and scale-less, neither ‘double- or several-waisted’)... 16

15(14).
  • social insects forming organized communities; the gaster concolorous; the adult populations including specialised, sterile females constituting ‘workers’ ... Formicidae
  • solitary insects; the gaster colour-patterned; the adult populations comprising males and fertile females only ... Tiphiidae

16(14).
  • Fore-wings combining greatly reduced venation with a conspicuous radial cell ... 17
  • Fore-wings not combining greatly reduced venation with a conspicuous radial cell... 18

17(16).
  • The second or second and third abdominal tergites representing at least half of the gaster ... Cynipidae
  • The second or second and third abdominal tergites representing less than half of the gaster ... Figitidae

18(16).
  • Fore-wings combining greatly reduced venation with a conspicuous, blind-ending stigmal vein ... 19
  • Fore-wings not combining greatly reduced venation with conspicuous stigmal vein... 29

19(18).
  • Pronotum long, extending back to the tegulae ... 20
  • Pronotum short, not extending back to the tegulae... 23

20(19).
  • Fore-wings with a conspicuous pterostigma ... 21
  • Fore-wings without a pterostigma... 22

21(20).
  • Antennae inserted above the lower margins of the eyes; antennae not geniculate; closed fore-wing cells 1 ... Proctotrupidae
  • Antennae inserted below the eyes; antennae geniculate; closed fore-wing cells 0 ... Ceraphronidae

22(20).
  • Mid and hind tibiae with one spur only ... Scelionidae
  • Mid and hind tibiae with two spurs ... Diapriidae

23(19).
  • Tarsi 3 segmented ... Trichogrammatidae
  • Tarsi 4 segmented ... Eulophidae
  • Tarsi 5 segmented... 24

24(23).
  • The mesepisternum large, more or less covering the mesepimeron (and the mid-tibial spur usually enlarged) ... Encyrtidae
  • The mesepisternum not enlarged to obscure the mesepimeron (and the mid-tibial spur rarely larger than the hind one)... 25

25(24).
  • The hind coxae five to six times the size of the front ones ... 26
  • The hind coxae not conspicuously larger than the front ones... 27

26(25).
  • Hind femur simple or 1-toothed beneath ... Torymidae
  • Hind femur with a row of teeth beneath ... Chalcididae

27(25).
  • Pronotum wide and quadrate, almost as wide as the (often coarsely punctured) mesoscutum ... 28
  • Pronotum usually narrower in front or transversely linear, narrower than the (usually reticulate) mesoscutum ... Pteromalidae

28(27).
  • Visible abdominal segments highly metallic in appearance; larvae with segmented legs ... Perilampidae
  • Visible abdominal segments not highly metallic; larvae legless or the legs vestigial ... Eurytomidae

29(18).
  • Fore-wings with the venation well developed ... 30
  • Fore-wings with very reduced venation... 85

30(29).
  • Mid tibiae with one spur ... 31
  • Mid tibiae with two spurs... 58

31(30).
  • Pronotum long, extending back to the tegulae ... 32
  • Pronotum short, not extending back to the tegulae... 45

32(31).
  • Hind femur with a clear trochantellus ... 33
  • Hind femur without a well defined trochantellus... 40

33(32).
  • The spiracle cover lobe of the pronotum margined with close fine hairs ... 34
  • The spiracle cover lobe of the pronotum not margined with close fine hairs... 38

34(33).
  • Hind-wings with an anal lobe ... 35
  • Hind-wings without an anal lobe... 36

35(34).
  • Hind-wings with closed cells; larvae legless or the legs vestigial ... Trigonalidae
  • Hind-wings without closed cells; larvae with segmented legs ... Evaniidae

36(34).
  • Hind-wings with closed cells; larvae legless or the legs vestigial ... Trigonalidae
  • Hind-wings without closed cells; larvae with segmented legs... 37

37(36).
  • The gaster with the first two segments fused ... Aulacidae
  • The gaster with the first two segments not fused ... Gasteruptiidae

38(33).
  • Fore-wings with a conspicuous pterostigma; pronotum vertically grooved to receive the fore femur; the abdomen not extremely laterally compressed and knife-like ... 39
  • Fore-wings without a pterostigma; pronotum not vertically grooved for reception of the fore femur (ignoring any grooving close to and parallel with the front margin); the abdomen very laterally compressed and knife-like ... Ibaliidae

39(38).
  • Hind-wings with the median cell elongated beyond the base of the marginal vein; fore-wings always exhibiting the linking cross-vein ‘distal 2 m cu’ ... Ichneumonidae
  • Hind-wings with the median cell terminating short of the base of the marginal vein; fore-wings never exhibiting the linking cross-vein ‘distal 2m cu’ ... Braconidae

40(32).
  • Hind tibiae with spurs specialised for a cleaning rôle ... 41
  • Hind tibiae without specialised spurs... 42

41(40).
  • Wings folded longitudinally when at rest ... Eumenidae
  • Wings not folding longitudinally ... Pompilidae

42(40).
  • The spiracle cover lobe of the pronotum margined with close fine hairs; closed fore-wing cells 6 to 10; ovipositor of females modified as a retractable sting ... 43
  • The spiracle cover lobe of the pronotum not margined with close fine hairs; closed fore-wing cells 2 to 3; ovipositor of females adapted for piercing ... Heloridae

43(42).
  • Eyes emarginate ... Sapygidae
  • Eyes ovate and not emarginate... 44

44(43).
  • Hind-wings with a notched ‘jugal’ lobe; thorax of the wingless females with distinct segmentation dorsally ... Tiphiidae
  • Hind-wings without a ‘jugal’ lobe; thorax of the wingless females without distinct segmentation dorsally ... Mutillidae

45(31).
  • Hind-wings with closed cells ... 46
  • Hind-wings without closed cells... 56

46(45).
  • Adults very hairy ... 47
  • Adults sparsely hairy... 54

47(46).
  • Labial palps with segments 1 and 2 much longer than the distal two, and flattened ... 48
  • Labial palps with all the segments similar in length and subcylindrical... 50
  • Labial palps with only segment 1 elongated and all of them subcylindrical ... Andrenidae

48(47).
  • The labrum longer than broad ... Megachilidae
  • The labrum broader than long... 49

49(48).
  • The adult populations including specialised, sterile females constituting ‘workers’ ... Apidae
  • The adult populations comprising males and fertile females only ... Anthophoridae

50(47).
  • The basal forewing vein (BV) markedly arched ... 51
  • The basal forewing vein (BV) straightish... 52

51(50).
  • Mentum and submentum present; tongue not pointed (emarginate, truncate or rounded) ... Colletidae
  • Mentum and submentum more or less absent; tongue pointed ... Halictidae

52(50).
  • Tongue pointed ... 53
  • Tongue not pointed (emarginate, truncate or rounded) ... Colletidae

53(52).
  • The terminal antennal segment pointed ... Andrenidae
  • The terminal antennal segment truncate ... Melittidae

54(46).
  • Visible abdominal segments highly metallic in appearance ... Xylocopidae
  • Visible abdominal segments not highly metallic... 55

55(54).
  • Hind basitarsi wider than the other segments ... Halictidae
  • Hind basitarsi not noticeably wider than the other segments ... Sphecidae

56(45).
  • Hind tibiae with spurs specialised for a cleaning rôle ... 57
  • Hind tibiae without specialised spurs ... Chrysididae

57(56).
  • Antennal segments 10 ... EmbolemidaeDryinidae
  • Antennal segments 11 to 15 ... BethylidaeEmbolemidae

58(30).
  • Pronotum long, extending back to the tegulae ... 59
  • Pronotum short, not extending back to the tegulae... 72

59(58).
  • Hind femur with a clear trochantellus ... 60
  • Hind femur without a well defined trochantellus... 67

60(59).
  • The spiracle cover lobe of the pronotum margined with close fine hairs ... 61
  • The spiracle cover lobe of the pronotum not margined with close fine hairs... 65

61(60).
  • Hind-wings with an anal lobe ... 62
  • Hind-wings without an anal lobe... 63

62(61).
  • Hind-wings with closed cells; larvae legless or the legs vestigial ... Trigonalidae
  • Hind-wings without closed cells; larvae with segmented legs ... Evaniidae

63(61).
  • Hind-wings with closed cells; larvae legless or the legs vestigial ... Trigonalidae
  • Hind-wings without closed cells; larvae with segmented legs... 64

64(63).
  • The gaster with the first two segments fused ... Aulacidae
  • The gaster with the first two segments not fused ... Gasteruptiidae

65(60).
  • Pronotum not vertically grooved for reception of the fore femur (ignoring any grooving close to and parallel with the front margin); fore-wings without a pterostigma; the abdomen very laterally compressed and knife-like ... Ibaliidae
  • Pronotum vertically grooved to receive the fore femur; fore-wings with a conspicuous pterostigma; the abdomen not extremely laterally compressed and knife-like... 66

66(65).
  • Hind-wings with the median cell elongated beyond the base of the marginal vein; fore-wings always exhibiting the linking cross-vein ‘distal 2 m cu’ ... Ichneumonidae
  • Hind-wings with the median cell terminating short of the base of the marginal vein; fore-wings never exhibiting the linking cross-vein ‘distal 2m cu’ ... Braconidae

67(59).
  • Hind tibiae with spurs specialised for a cleaning rôle ... 68
  • Hind tibiae without specialised spurs... 69

68(67).
  • Wings folded longitudinally when at rest; social insects forming organized communities; the adult populations including specialised, sterile females constituting ‘workers’ ... Vespidae
  • Wings not folding longitudinally; solitary insects; the adult populations comprising males and fertile females only ... Pompilidae

69(67).
  • The spiracle cover lobe of the pronotum margined with close fine hairs; closed fore-wing cells 6 to 10; ovipositor of females modified as a retractable sting ... 70
  • The spiracle cover lobe of the pronotum not margined with close fine hairs; closed fore-wing cells 2 to 3; ovipositor of females adapted for piercing ... Heloridae

70(69).
  • Eyes emarginate ... Sapygidae
  • Eyes ovate and not emarginate... 71

71(70).
  • Hind-wings with a notched ‘jugal’ lobe; thorax of the wingless females with distinct segmentation dorsally ... Tiphiidae
  • Hind-wings without a ‘jugal’ lobe; thorax of the wingless females without distinct segmentation dorsally ... Mutillidae

72(58).
  • Hind-wings with closed cells ... 73
  • Hind-wings without closed cells... 83

73(72).
  • Adults very hairy ... 74
  • Adults sparsely hairy... 81

74(73).
  • Labial palps with segments 1 and 2 much longer than the distal two, and flattened ... 75
  • Labial palps with all the segments similar in length and subcylindrical... 77
  • Labial palps with only segment 1 elongated and all of them subcylindrical ... Andrenidae

75(74).
  • The labrum longer than broad ... Megachilidae
  • The labrum broader than long... 76

76(75).
  • The adult populations including specialised, sterile females constituting ‘workers’ ... Apidae
  • The adult populations comprising males and fertile females only ... Anthophoridae

77(74).
  • The basal forewing vein (BV) markedly arched ... 78
  • The basal forewing vein (BV) straightish... 79

78(77).
  • Mentum and submentum present; tongue not pointed (emarginate, truncate or rounded) ... Colletidae
  • Mentum and submentum more or less absent; tongue pointed ... Halictidae

79(77).
  • Tongue pointed ... 80
  • Tongue not pointed (emarginate, truncate or rounded) ... Colletidae

80(79).
  • The terminal antennal segment pointed ... Andrenidae
  • The terminal antennal segment truncate ... Melittidae

81(73).
  • Visible abdominal segments highly metallic in appearance ... Xylocopidae
  • Visible abdominal segments not highly metallic... 82

82(81).
  • Hind basitarsi wider than the other segments ... Halictidae
  • Hind basitarsi not noticeably wider than the other segments ... Sphecidae

83(72).
  • Hind tibiae with spurs specialised for a cleaning rôle ... 84
  • Hind tibiae without specialised spurs ... Chrysididae

84(83).
  • Antennal segments 10 ... DryinidaeEmbolemidae
  • Antennal segments 11 to 15 ... EmbolemidaeBethylidae

85(29).
  • Fore-wings with a conspicuous pterostigma ... 86
  • Fore-wings without a pterostigma... 88

86(85).
  • Hind femur with a clear trochantellus; larvae with segmented legs ... 87
  • Hind femur without a well defined trochantellus; larvae legless or the legs vestigial ... Proctotrupidae

87(86).
  • Hind-wings with the median cell elongated beyond the base of the marginal vein; fore-wings always exhibiting the linking cross-vein ‘distal 2 m cu’ ... Ichneumonidae
  • Hind-wings with the median cell terminating short of the base of the marginal vein; fore-wings never exhibiting the linking cross-vein ‘distal 2m cu’ ... Braconidae

88(85).
  • Pronotum long, extending back to the tegulae; hind femur without a well defined trochantellus; the wings not long-fringed; insects associated with plant galls; hind-wings not linear and not basally stalked ... Platygastridae
  • Pronotum short, not extending back to the tegulae; hind femur with a clear trochantellus; the wings marginally very long-fringed, the fringes as long as or almost as long as the width of the wing; insects not associated with galls; hind-wings linear and basally stalked or reduced to the linear stalk ... Mymaridae


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: the families of Hymenoptera. Version: 16th May 2016. delta-intkey.com’.

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