Tabanid adults are stout-bodied flies. They can generally be distinguished as horse flies or deer flies based on several morphological characteristics (see Table 1). The antennae are prominent and extent anteriorly. In general, they possess a fairly large size, striking appearance and diurnal habits. The eyes of many species are brilliantly patterned with shades of green, yellow, orange, and violet. They often consist of large ommatidial facets dorsally and smaller facets ventrally. For further details on morphology see e.g., Mullens (2002).
The developmental cycle includes the following stages: Egg, 1-3 mm long, which are deposited in masses; larva (predaceous and cannibalistic), performing 6-13 larval molts with larvae overwintering; a pupal stage and the adult stage. Some tabanids can develop from egg to adult in as little as 6 weeks, whereas in other species, 2 to 3 years may be spent as larvae, depending on environmental conditions etc. Tabanid mating occurs in flight, especially in the morning.
Table 1: Morphological characteristics used to differentiate adult horse and deer flies (Mullens, 2002)
Horse flies (e.g., Tabanus)
Deer flies (e.g., Chrysops)
Short, base of flagellum greatly enlarged
Long, base of flagellum not greatly enlarged
Vestigial or lacking
Clear, uniformly cloudy or spotted
Apical spurs on hind tibiae
- Mullens BA: Horse flies and deer flies (Tabanidae). In: Mullen G, Durden L (eds.): Medical and Veterinary Entomology. 2002, Academic Press, London, pp 263-77