British insects: water beetles


L. Watson and M. J. Dallwitz

This data set is generated from a DELTA database (Dallwitz 1980; Dallwitz, Paine and Zurcher 1993), and forms part of our ‘British Insects’ ( suite of packages. These all incorporate descriptive data organized under the DELTA system, and in addition to presenting hundreds of scans of classic early illustrations with updated nomenclature, they purport to offer facilities for attempting at least partial identification and for taxonomic information retrieval, via the interactive program Intkey.

The present package includes all the genera of Coleoptera usually recognised as or including ‘water beetles’, described via standard morphological and ecological characters and extensively illustrated. Family descriptions of Chrysomelidae and Curculionidae are also included, because the former encompasses forms (subfamily Donaciinae) with genuinely aquatic larvae, and both families include numerous species associated with helophytic plants, the adults of which, though not truly aquatic, are often found in the water. The comparative descriptions compiled for our ‘Families of British Coleoptera’ (, including full references) have here been extended, mainly with reference to the keys and descriptions in Joy’s Practical Handbook of British Beetles (1932, necessitating much updating of his family and generic names); the detailed, illustrated keys and superficial taxon descriptions provided by Friday (1988) and Foster and Friday (2011); Balfour-Brown’s three volumes (1940, 1950 and 1958); and the Delta descriptions of ‘Beetle larvae of the world’ provided by Lawrence et al. (1999).

Sources of illustrations are listed in the References, and discussed in some detail in the Introduction to our Families of British Coleoptera; and in the present context, additional scans from Joy’s line drawings have permitted representing nearly all the genera by at least one illustration. The Coleoptera Introduction also gives information on laborious updating of the nomenclature, without which the splendidly illustrated, classic works of Curtis (see Updated insect names for John Curtis’s British Entomology) and Fowler (see Coleoptera of the British Islands) are now almost useless for practical applications. We hope that the recently applied names provided here with the fine Curtis and Fowler illustrations will facilitate their use in connection with modern texts.

Detailed, properly comparative taxon descriptions are the life blood of competent taxonomy, being essential both for competent assessments of revised classifications and for reliable identification; but with the notable exception of Lawrence et al., few practitioners since the early 20th century have bothered to provide them, notwithstanding extensive changes in taxon circumscriptions. Current publications intended for identifying British water beetles conform with this unfortunate practice, offering keys accompanied only by illustrations and brief, pseudo-diagnostic descriptive comments which are simply inadequate for confirming putative identifications. Consequently, in the absence of original observations, the present compilation is unlikely to achieve its taxonomic objectives satisfactorily. However, even in its present form, it should suffice to demonstrate the superiority of interactive identification and information retrieval over hard copy; and like all the compilations in this ‘British Insects’ series, organization under the Delta system ensures ready access for improving the data and making corrections. Informed criticism and constructive input are of course welcome, and will be appropriately acknowledged. Alternatively, the complete data sets can be donated if required for teaching purposes, or to any professional or amateur entomologist or organization interested in developing them further.