The seasonal distribution of biting flies in St. Mary’s County, Maryland in 1975 (Diptera: Tabanidae, Muscidae)

In 1974, an outbreak of equine infectious anaemia (swamp fever) occurred in St. Mary’s County, Maryland. From a survey in 1975 at 3 of the places affected, 47 species of tabanids and 2 muscids are listed that were collected in box and canopy traps and by net sweeps overhead or near horses. Eight species of which more than 100 examples were taken were considered to be important in one or more areas. Tabanus quinquevittatus Wied. and T. sulcifrons Macq. were abundant in all 3 areas and were frequently collected from horses. Stomoxys calcitrans (L.) was an abundant pest of horses. Attacks on horses were most severe in August. The seasonal and geographical distribution of the more important species are discussed in relation to biological and ecological factors. The peaks of abundance of 6 of the most abundant species in 1975 coincided with the onset of equine infectious anaemia in 1974, and it is suggested that biting flies may have played a part in the transmission of the disease.