Tabanids and their medical importance
Andreas Krueger
German Armed Forces – Hospital Hamburg, Dept. Tropical Medicine at the Bernhard Nocht Institute for Tropical Medicine, Labgroup Medical Entomology. Bernhard-Nocht Str. 74, 20359 Hamburg, Germany
Tabanids (clegs, horse flies, deer flies) belong in the order Diptera to the “low” infraorder Tabanomorpha and are represented with over 3500 species worldwide, predominantly in the tropics.
Most of the 160 or so European species are confined to the Mediterranean area. Only the females feed blood on mammals including humans. They are usually diurnal and exophilic as well as
exophagous. They develop in (semi-)aquatic or terrestrial habitats. The optical remote perception of the host is steered by large, dark, heat-emitting objects (also cars!). Tabanids are good and fast
fliers, and a potential host is pursued actively by them.
Adult Tabanus species can be larger than 2 cm. The eyes of many tabanids have a species-specific, brightly coloured pattern of spots or stripes. For Chrysops species dark-brownish wing patterns are
characteristic, while in Haematopota species the wings are greyishly mottled and typically kept roof-like over the abdomen. In particular, the clearly segmented antennae distinguish tabanids from
“higher” flies. The mouthparts superficially resemble the sponging labella of the cyclorrhaph flies.
However, they accommodate stylet-like mandibles and laciniae for piercing the host skin, which leads straight to their medical and economic importance: on one hand the robust proboscis causes
quite painful bites and leaves, on the other hand, relatively large, after-bleeding wounds. These can attract other flies and be thus entrance gates for various secondary infections. In addition, the saliva may cause toxic effects. A massive nuisance of domestic animals can lead to growth inhibition and
reduced milk production. Of special interest is the role of tabanids in the cyclic or mechanical transmission of pathogens to humans and animals. Some Chrysops spp. act as obligatory vectors of
the filaria Loa loa (Nematoda: Spirurida, Onchocercidae), the causative agent of human loiasis disease in Central Africa, where approx. 10 million humans are infected. By migrating of the adult
female worms in the connective tissue (hence the German name „Wanderfilarie“) it comes to swelling („Calabar“- or „Cameroon swelling“) as well as to provoking of the eyes, if the worm
moves under the conjunctiva.
Experimental data suggest the possibility of the mechanical transmission of numerous pathogens,
but the situation in the field is widely unclear. Due to the specific behaviour of tabanids, i) short time feeder (at least Tabanus spp.), ii) causing after-bleeding wounds, iii) predominant zoophily,
and the association of high population densities during respective disease outbreaks, at least a veterinary meaning must be derived for viruses (equine infectious anemia virus, EIA virus), for bacteria (Bacillus anthracis, Francisella tularensis) as well as for certain protozoa of the genus Trypanosoma. Regarding anthrax only once from India species-related data were given for an outbreak, whereby Tabanus indianus, T. bicinctus (=T. biannularis) and Haematopota montana were incriminated. Eventually, in South America tabanids can act as phoretic vehicles for the eggs
of the myiasis-causing human bot-fly Dermatobia hominis.