This handbook covers British species of the family Dolichopodidae, popularly called long-legged flies. These are often attractive both visually and in their behaviour so the larger species will be familiar to most naturalists. The sexes are often strongly dimorphic, males having their legs and wings modified for signalling during sometimes complex courtship. Both the larvae and adults are predators, with the exception of one genus whose larvae are miners within monocotyledons. Most species are associated with wetlands from the sea shore to montane pools, while a small number have more xerophilic tendencies and others are associated with rot-holes or wood-boring beetles. Dolichopodids can play an important role in nature conservation assessment of sites as their habitat affinities, rarity status and distributions are fairly well known. This book focuses on the British fauna of about 327 species in 47 genera placed in 12 subfamilies. One species so far found only in Ireland is also included. The limits of several subfamilies are poorly defined, and phylogenetic relationships based on morphological and molecular data are also not always in agreement so the placement in this book of some genera differs from previous British checklists. In particular, some genera are assigned to the Peloropeodinae which has not been accepted previously in the British literature. Owing to their secondary sexual characteristics, males are easier to identify than females so separate keys are provided for nearly all genera. Some males can be separated reliably only by using genitalia characters which are therefore often included in the keys and are illustrated for most species. In a few cases no reliable differences have been found for females. Line drawings illustrate many of the characters mentioned in the couplets and photographs show representative species of all genera. Most keys are derived de novo rather than updating those already existing. Species accounts briefly describe the most important characters to confirm the identification arrived at using the key, distinctions from similar species that may occur in Britain, the distribution in Britain, and their habitat associations.
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