Insects of Britain and Ireland: the families of Hymenoptera

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L. Watson and M. J. Dallwitz

Character list

#1. <Nomenclature:>/

~ (‘alternatively’) is here used to indicate ‘sometimes not unreasonably included in or reduced to’.

#2. <Common name(s) of family members:>/

#3. Adults <size, exclusive of ovipositor: see Notes>/

1. minute <up to 4 mm long>/

2. small <4–8 mm long>/

3. medium sized <8–14 mm long>/

4. large <i.e., in the context of Hymenoptera: at least 14 mm long>/

Accurate measurements for most families are hard to come by, and the data reflected in this character (see the adjoining one in the ‘natural order’ version of the character list) are unreliable. On the other hand, it is absurd to ignore for identificatory purposes the large differences in size between (for example) bumble-bees and cynipids. At early stages of an identification, some useful separation will sometimes be achieved, while showing due caution, by entering two or more adjoining states of this character (e.g., 1–2 or 3–4).

#4. Adults <length: front of head to extremity of abdomen, excluding ovipositor. See Notes>/

mm long/

Most of the length data recorded here are quoted from general accounts of the families, and accurate measurements reflecting their British species contents have not yet been entered. However, while the recorded ranges are unreliable in detail for identificatory purposes, the ranges given are likely to exceed the true level of variation. When pursuing identifications, therefore, failure to separate families via this character should be a more likely outcome than erroneous assignment.

#5. Adults <whether with a spherical head on a long neck>/

1. conspicuously bearing a spherical head on an elongated ‘neck’/

2. not conspicuously spherical-headed and ‘necked’ <implicit>/

#6. Adults <hairiness>/

1. very hairy/

2. sparsely hairy/

#7. Adults <hair structure>/

1. with branched or feathery hairs on the body <at least near the tegulae>/

2. with only simple hairs on the body/

#8. Insects <whether species are associated with galls>/

1. associated with plant galls <whatever the nature of the association>/

2. not associated with galls/

#9. <Insects, whether social or solitary:>/

1. social insects forming organized communities/

2. solitary insects <implicit>/

‘Social’: implies social organisation. Insects which merely form colonies of nests in close proximity are treated as ‘solitary’.

#10. The adult populations <whether including sterile females, or ‘workers’>/

1. including specialised, sterile females constituting ‘workers’/

2. comprising males and fertile females only <implicit>/


#11. Eyes <shape>/

1. emarginate/

2. ovate and not emarginate/

#12. Sub-antennal grooves <presence>/

1. present <to accommodate the laterally and somewhat ventrally directed antennal scape>/

2. absent <implicit: the usual condition>/

#13. Antennal segments <number>/

#14. The terminal antennal segment <shape>/

1. pointed/

2. truncate/

#15. Antennae <height of insertion>/

1. inserted above the lower margins of the eyes <implicit>/

2. inserted below the eyes/

#16. Antennae <relative length of third segment>/

1. with a very elongated third segment/

2. without noticeable elongation of the third segment <implicit>/

#17. Antennae <whether geniculate>/

1. geniculate/

2. not geniculate/

#18. The antennal flagellum <simple or serrate>/

1. serrate via distinctly produced segments/

2. simple and not serrate, the segments not produced/

#19. The labrum <relative shape>/

1. longer than broad/

2. broader than long/

#20. Tongue <glossa: relative length>/

1. longer than the prementum/

2. shorter than the prementum/

#21. Tongue <glossa: shape>/

1. pointed/

2. not pointed <emarginate, truncate or rounded>/

#22. Labial palps <form>/

1. with segments 1 and 2 much longer than the distal two, and flattened/

2. with all the segments similar in length and subcylindrical/

3. with only segment 1 elongated and all of them subcylindrical/

#23. Mentum and submentum <presence>/

1. present/

2. more or less absent/

#24. The mandibles <form>/

1. long and crossed over when at rest/

2. short and stout, meeting more or less on the mid-line/


#25. Thorax <colour>/

#26. Thorax of the wingless females <segmentation>/

1. with distinct segmentation dorsally/

2. without distinct segmentation dorsally/

#27. Pronotum <whether hind margin straight or emarginate>/

1. more or less straight at the back/

2. deeply indented or emarginate at the back/

#28. Pronotum <whether extending back to the tegulae>/

1. long, extending back <more or less> to the tegulae/

2. short, not extending back to the tegulae/

#29. Pronotum <form>/

1. wide and quadrate, almost as wide as the (often coarsely punctured) mesoscutum/

2. usually narrower in front or transversely linear, narrower than the (usually reticulate) mesoscutum/

#30. Pronotum <lateral grooves>/

1. not vertically grooved for reception of the fore femur <though often grooved close to and parallel with the front margin>/

2. vertically grooved to receive the fore femur/

#31. The spiracle cover lobe of the pronotum <whether hair-margined>/

1. margined with close fine hairs/

2. not margined with close fine hairs/

#32. Mesoscutellum <whether separated from the scutum>/

1. completely separated from the scutum laterally by defined axillae/

2. not separated from the scutum laterally, axillae not defined/

#33. Mesopleuron <presence of suture>/

1. with an oblique suture/

2. without a suture/

#34. The mesepisternum <relative size>/

1. large, more or less covering the mesepimeron (and the mid-tibial spur usually enlarged)/

2. not enlarged to obscure the mesepimeron (and the mid-tibial spur rarely larger than the hind one)/

#35. Cenchri <presence>/

1. present/

2. absent/

‘Cenchri’: paired anterolateral protrusions from the metanotum, which are universally stated to be present in all Symphyta except Cephidae.

They are here recorded as lacking from all the families of Apocrita, although their absence is never explicitly recorded in the literature seen (exemplifying, yet again, the non-comparative inadequacy of routine taxonomic descriptive technique).

#36. Wings <presence>/

1. present <implicit>/

2. absent/

#37. The wings <conspicuous fringing>/

1. marginally very long-fringed <the fringes as long as or almost as long as the width of the wing>/

2. <fringed or not, but> not long-fringed <implicit>/

#38. Wings <folding>/

1. folded longitudinally when at rest/

2. not folding longitudinally/

#39. Fore-wings <presence of a pterostigma>/

1. with a conspicuous pterostigma/

2. without a pterostigma/

#40. Fore-wings <whether with well developed venation>/

1. with the venation well developed/

2. with very reduced venation/

#41. Fore-wings <with reduced venation, conspicuousness of stigmal vein>/

1. combining greatly reduced venation with a conspicuous, blind-ending stigmal vein/

2. not combining greatly reduced venation with conspicuous stigmal vein/

#42. Fore-wings <conspicuousness of radial cell>/

1. combining greatly reduced venation with a conspicuous <triangular or trapezoidal> radial cell/

2. not combining greatly reduced venation with a conspicuous radial cell/

#43. Fore-wings <cross-venation> <Braconidae/Ichneumonidae>/

1. never exhibiting the linking cross-vein ‘distal 2m cu’ <Braconidae>/

2. always exhibiting the linking cross-vein ‘distal 2 m cu’ <Ichneumonidae>/

#44. Closed fore-wing cells <number>/

#45. Submarginal cells <of fore-wings, number>/

#46. Discoidal cells <of fore-wings, number>/

#47. The basal forewing vein (BV) <layout>/

1. markedly arched/

2. straightish/

#48. Hind-wings <shape>/

1. linear and basally stalked or reduced to the linear stalk/

2. not linear and not basally stalked <implicit>/

#49. Hind-wings <whether with complete venation>/

1. with the venation relatively well developed/

2. with very reduced venation/

#50. Hind-wings <presence of cells>/

1. with closed cells <discounting a narrow costal cell>/

2. without closed cells <other than a narrow costal one>/

#51. Hind-wings <elongation of the median cell>/

1. with the median cell elongated beyond the base of the marginal vein <Ichneumonidae>/

2. with the median cell terminating short of the base of the marginal vein <Braconidae>/

#52. Hind-wings <presence of ‘jugal’ lobe>/

1. with a notched ‘jugal’ lobe/

2. without a ‘jugal’ lobe/

#53. Hind-wings <presence of an anal lobe>/

1. with an anal lobe/

2. without an anal lobe/

#54. The hind coxae <relative size>/

1. five to six times the size of the front ones/

2. not conspicuously larger than the front ones/

#55. Mid and hind tibiae <number of spurs>/

1. with one spur only/

2. with two spurs/

#56. Mid tibiae <one or two spurs>/

1. with one spur/

2. with two spurs/

#57. Fore tibiae <spur, straight or curved>/

1. with a straight spur/

2. with a curved spur <calcar>/

#58. Fore femur <whether dilated>/

1. dilated/

2. not noticeably dilated/

#59. Hind femur <whether toothed below>/

1. toothed below/

2. not toothed below/

#60. Hind femur <trochantellus>/

1. with a clear trochantellus/

2. without a well defined trochantellus/

‘Trochantellus’: ostensibly an articulated, additional segment of the trochanter (q.v.), but actually the proximal end of the femur. It is detectable in most Hymenoptera, but is larger and more freely articulated in Symphyta and parasitic Apocrita.

‘Trochanter’: a short segment of the leg, interposed between the coxa and the femur.

#61. Hind femur <toothing>/

1. simple or 1-toothed beneath/

2. with a row of teeth beneath/

#62. Hind tibiae <whether curved around the femora>/

1. conspicuously curved around the femora/

2. not curved around the femora/

#63. Hind tibiae <presence of specialised spurs>/

1. with spurs specialised for a cleaning rôle <see Notes>/

2. without specialised spurs <spur-less, or with unspecialised spurs>/

The data in tibial spurs as compiled here are unsatisfactory, in the absence of unambiguous comparative data on their occurrence on fore-, mid- and hind-legs of Hymenoptera in general.

A modified distal tibial spur (‘calcar’) occurs on the fore-legs of many Hymenoptera, and in association with a brush of hairs (‘strigil’) borne in an emargination of the basitarsus constitutes an elegant cleaning mechanism for the antennae. On hind legs, calcars are seemingly restricted to the supposedly highly evolved families constituting the Aculeata, where they are used to clean the gaster, wings and mid-legs. Here, either a calcar is developed from the hind tibial spur, or both spurs are variously modified, and the cleaning mechanism is completed by a dense brush of hairs on the inner distal surface of the tibia and sometimes on the basitarsus.

#64. Tarsi <number of segments>/


#65. Hind basitarsi <whether wider than the other tarsal segments>/

1. wider than the other segments/

2. not noticeably wider than the other segments/


#66. The abdomen <whether sessile or basally constricted>/

1. broadly sessile at its base, without a marked constriction <the insects not noticeably ‘waisted’: Symphyta>/

2. with a marked basal constriction <the insects ‘waisted’: Apocrita>/

#67. The abdomen <basally constricted, whether long-petiolate>/

1. long petiolate/

2. short-waisted/

#68. The ‘waist’ <or ‘petiole’, whether with scales or nodes>/

1. with scales or nodes <including insects appearing ‘double- or several-waisted’>/

2. simple <node-less and scale-less, insects not ‘double- or several-waisted’: implicit>/

#69. The abdomen <whether extremely laterally compressed>/

1. very laterally compressed and knife-like/

2. not extremely laterally compressed and knife-like <implicit>/

#70. Visible abdominal segments <number>/

#71. The gaster <fusion of segments>/

1. with the first two segments fused/

2. with the first two segments not fused/

#72. The second or second and third abdominal tergites <contribution to the gaster>/

1. representing at least half of the gaster/

2. representing less than half of the gaster/

#73. Visible abdominal segments <whether metallic>/

1. highly metallic in appearance/

2. not highly metallic/

#74. The gaster <whether concolorous>/

1. concolorous/

2. colour-patterned/

#75. The gaster <when concolorous, colour>/

#76. The gaster <when not concolourous, colours>/

#77. The gaster <position of attachment>/

1. attached high on the propodeum/

2. attached low on the propodeum/

#78. Ovipositor of females <whether visibly protruding>/

1. visibly protruding/

2. not visibly protruding <i.e., retractable>/

#79. Ovipositor of females <constitution>/

1. adapted for piercing/

2. adapted for boring/

3. adapted as a saw/

4. modified as a retractable sting/

5. greatly reduced/


#80. Larvae <whether with legs>/

1. with segmented <thoracic> legs <usually also with abdominal legs>/

2. legless or the legs vestigial/

#81. Larvae <life style. See Notes>/

1. phytophagous/

2. parasitic on hosts selected by the mother/

3. predacious <in situations and on victims pre-determined by the mother>/

4. feeding on prey collected and stored by the adults/

5. feeding on material manufactured by the adults/

Note the essential distinction to be made between “parasitic”, referring to the general life-style of a species (q.v.); and the same term when it relates, as here, to the feeding habits of individuals. The different concepts are often confused in entomological literature.

In practice, the distinction between “parasitic” and “predatory” is not at all clear. In any case, the requisite details are sometimes elusive, the insects’ behaviour can be complex and hard to categorise, and there may be considerable variations on themes within individual families. In Apocrita-Parasitica and “socially parasitic” bees in particular, where the usual definitions of parasitism versus predation tend to break down, behaviour referable to the one condition sometimes succeeds the other.

#82. Larvae <association with galls>/

1. primary inducers of galls/

2. parasitic on other gall occupants <‘lodgers’ in existing galls>/

3. predacious on other gall occupants <‘lodgers’ in existing galls>/

General comments.

#83. <General comments:>/

British representation.

#84. Species in Britain <number>/

#85. <Genera in Britain:>/


#86. Suborder/

1. Symphyta <sawflies>/

2. Apocrita/

#87. Series <of Apocrita>/

1. Parasitica/

2. Aculeata <bees, ants and wasps>/

#88. Superfamily <of Symphyta>/

1. Xyeloidea/

2. Megalodontoidea/

3. Siricoidea/

4. Orussoidea/

5. Cephoidea/

6. Tenthredinoidea/

#89. Superfamily <of Apocrita>/

1. Trigonaloidea/

2. Ichneumonoidea/

3. Evanioidea/

4. Cynipoidea/

5. Chalcidoidea/

6. Proctotrupoidea/

7. Ceraphronoidea/

8. Chrysidoidea <including Bethyloidea>/

9. Scolioidea/

10. Formicoidea/

11. Pompiloidea/

12. Vespoidea/

13. Sphecoidea/

14. Apoidea/

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.’.