Elateriformia (Coleoptera) Larvae
The Eucnemidae is a cosmopolitan family.
Most eucnemid larvae occur in dead wood, but it is not certain what food source they utilize. The mouthparts are of a liquid-feeding type, but the mandibles are incapable of opposition, making predation unlikely. It is probable that the woody substrate is broken down extra-orally and the chemical products consumed.
Böving, A. G. and Craighead, F. C. (1931). An illustrated synopsis of the principal larval forms of the order Coleoptera. Entomologica Americana (New Series) 1: 1–351, 125 pls.
Burakowski, B. (1989). Hypermetamorphosis of Rhacopus attenuatus (Maeklin) (Coleoptera, Eucnemidae). Annales Zoologici, Warsaw 42: 165–180.
Becker, E. C. (1991). Eucnemidae (Elateroidea), pp 419–421 in Stehr, F. W. (ed.), Immature Insects. Vol. II. Kendall Hunt: Dubuque, Iowa.
Costa, C., Vanin, S. A. and Casari-Chen, S. A. (1988). Larvas de Coleoptera do Brasil, vi + 282 pp. Museu de Zoologia, Universidade de Sao Paulo: Sao Paulo.
Gardner, J. C. M. (1935). Immature stages of Indian Coleoptera (17). (Eucnemidae). Indian Forest Records (New Series) Entomology 1: 79–93, pls 1–2.
Body. Length less than 3 mm to more than 15 mm. Body not broadly ovate and strongly flattened; relatively straight or only slightly curved ventrally; circular in cross-section to strongly flattened; body, as viewed from above elongate and more or less parallel-sided, or oblong to ovate, not parallel-sided. Vestiture consisting of fine hairs or setae only. Dorsal surfaces more or less heavily pigmented or sclerotized, or very lightly pigmented or sclerotized; generally smooth. Ventral surfaces more or less heavily pigmented, or very lightly pigmented.
Head. Head prognathous or slightly declined; protracted or slightly retracted; not concealed from above by prothorax; narrower than thorax; not forming sclerotized, serrate, wedge-like plate, or forming sclerotized, serrate, wedge-like plate. Head capsule strongly depressed and wedge-like anteriorly; posterior edge of head capsule not or only slightly emarginate. Median epicranial region without longitudinal furrow. Epicranial stem absent or very short. Frontal arms absent. Median endocarina absent or coincident with epicranial stem. Paired endocarinae absent or coincident with frontal arms. Number of stemmata zero. Number of antennal segments two. Ratio of antennal length to head width less than 0.15. Sensorium(a) on preapical antennal segment present; shorter than apical segment, or as long as or longer than apical segment. Sensorium(a) on preapical (or apical) antennal segment conical or palpiform. Antennal base without eversible membranous lobe. Frontoclypeal suture absent or vaguely indicated. Labrum completely fused to head capsule (suture absent); without crenulate emargination. Epipharyngeal rods absent. Mouthparts not forming sucking tube. Mandibles symmetrical; non-opposable, straight or curving laterally at apex; not approximate, diverging and longitudinally divided; absent or fused to head capsule, or broad and stout or more or less wedge-like; without groove or perforation. Apex of mandible narrow when viewed from in front (parallel or oblique to plane of movement); with single lobe or tooth. Accessory ventral process of mandible absent. Incisor edge of mandible simple, or with 1 or 2 subapical teeth. Mesal surface of mandibular base simple or slightly expanded. Mandibular mola absent. Ventral mouthparts retracted, or strongly protracted. Cardo absent, indistinct or membranous. Cardines or maxillary bases separated from each other by labium. Stipes longer than wide, or wider than long. Maxillary articulating area absent. Maxilla without apical lobes. Number of segments in maxillary palp three, or zero. First segment of maxillary palp without digitiform appendage. Labium consisting of single plate, or consisting of prementum and postmentum. Mentum, postmentum or labial plate completely or almost completely connate with maxillae, or partly or completely fused with maxillae (sutures incomplete or absent). Postmentum or labial plate subquadrate or trapezoidal, with blunt posterior edge. Postmentum or labial plate not divided longitudinally. Ligula absent. Number of segments in labial palp one, or two, or zero. Labial palps contiguous or separated by less than width of first palp segment. Hypopharyngeal sclerome absent. Hypostomal region present (separating labium from thorax). Hypostomal rods absent, or present (1 pair); extending to posterior edge of head; diverging posteriorly. Ventral epicranial ridges absent. Gula absent, or longer than wide; gular sutures absent, or separate. Gula or gular region fused to labium. Occipital foramen not divided by tentorial bridge.
Thorax. Prothorax not or only slightly wider than abdomen, or much wider than abdomen; not longer than meso- and metathorax combined. Thoracic terga without patches of asperities, or with patch(es) of asperities on metathorax only; without rows of asperities or carinae. Protergum without sclerotized plates, or with 1 or more sclerotized plates. Meso- and metaterga without sclerotized plates. Thorax without well-developed lateral tergal processes. Prosternum without armature, or with rod-like sclerotization. Mesocoxae or coxal lobes separated by more than 2 basal coxal diameters. Thoracic legs absent or represented by non-articulated lobes or processes, or articulated. Number of segments in mesothoracic leg one, or two, or three, or four, or five including pretarsus (claw), or zero. Number of segments in mesothoracic leg five or fewer including pretarsus (claw). Legs highly reduced, less than 0.2 times as long as head width. Metathoracic leg about same size as mesothoracic leg. Meso- and metathoracic legs not forming stridulatory organ. Apical segment of leg acute and claw-like (or consisting of 2 claws). Number of movable pretarsal claws one. Number of setae on pretarsus zero. Thoracic spiracles biforous or bilabiate; not placed at ends of spiracular tubes.
Abdomen. Ratio of length of abdomen (without appendages) to length of thorax more than 2.0. Number of visible abdominal segments ten, or nine. Abdominal terga not extending laterally beyond edges of sterna; without patches of asperities, or with patches of asperities on 1 or more segments; without rows of asperities. Abdomen without well-developed lateral processes. Abdominal tergum 3 without transverse dorsal folds or lobes; simple, not divided into transverse dorsal folds or lobes. Paired abdominal glands (openings or porous plates) absent. Dorsal, balloon-like tracheal gills absent. Long and narrow, lateral gills absent. Abdominal sterna without patches of asperities, or with patches of asperities on 1 or more segments; without rows of asperities. Paired ventral prolegs (or asperity-bearing ampullae) absent. Ventral abdominal gill tufts absent. Abdominal tergum 8 without special armature. Abdominal apex without respiratory chamber. Abdominal segment 9 excluding appendages shorter than segment 8, or as long as or slightly longer than segment 8. Abdominal tergum 9 not forming articulated plate; completely dorsal, or extending onto ventral surface; without paired processes or urogomphi, or with paired processes or urogomphi; with single pit between urogomphi; without median process or terminal disc. Ratio of length of urogomphus to basal width of tergum 9 less than 0.2, or between 0.2 and 1.0. Urogomphi fixed at base; unsegmented; bifurcate or with accessory processes; posteriorly oriented; separated by more than 2 basal widths. Abdominal sternum 9 partly or entirely exposed; simple or apparently absent, or with more than 6 basal asperities on each side; not enclosed by sternum 8, or partly or almost completely enclosed by sternum 8. Row of basal asperities on sternum 9 strongly curved posteriorly at sides; broadly interrupted at middle. Abdominal apex without hinged operculum. Abdominal segment 10 without oval lobes separated by longitudinal groove; concealed from above, sometimes membranous or more or less fused to segment 9, or distinct and visible from above; without asperated, tubular holdfast organs. Paired pygopods on segment 10 absent. Anal region posteriorly or terminally oriented, or ventrally oriented. Anal gill tufts absent. Anal hooks absent. Anterior abdominal spiracles biforous or bilabiate. Abdominal spiracles not placed at ends of spiracular tubes. Eighth abdominal spiracles functional and about the same size as others on abdomen; abdominal spiracle 8 lateral or dorsolateral, facing laterally.
Illustrations. • Dromaeolus. • Isorhipis.
The interactive key provides access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting specified attributes, and summaries of attributes within groups of taxa.
Cite this publication as: ‘Lawrence, J.F., Hastings, A.M., Dallwitz, M.J., Paine, T.A., and Zurcher, E.J. 1995 onwards. Elateriformia (Coleoptera) larvae: descriptions, illustrations, identification, and information retrieval for families and subfamilies. Version: 9th October 2005. http://delta-intkey.com’.