A Study of the Blackfly, Simulium ornatum Mg. (Diptera), with particular Reference to its Activity on Grazing Cattle

Abstract

SummarySamples of aquatic stages, taken from a small lowland stream near Durham, England, showed that the blackfly, Simulium ornatum Mg., emerged in quantity from April to October (7 months) and that oviposition took place between May and October. Oviposition was confined to the period between sunset and dusk.Flies emerging in the early summer of 1952 were smaller than those emerging in the spring and late summer of that year.S. ornatum landed on cattle from dawn to dusk, with usually a small peak 2–4 hrs. after dawn, and a large peak between sunset and dusk on warm, sunny days. On cool, cloudy days the number of flies landing showed irregular fluctuations throughout the day.The number of flies landing on untethered cattle was not markedly dependent on air temperature or saturation deficiency. Winds of over 5 m.p.h. markedly decreased or inhibited landing activity.On average about 70 per cent, of all blackflies landing spent less than 10 min. on cattle after landing, and this interval sometimes decreased as the total number of flies landing per unit time increased.Of the flies which landed, some 8 to 25 per cent, were calculated to bite the cow, and the proportion which bit varied significantly from day to day. The number of bites sustained by cattle in the district appeared to cause no ill-effect, apart from the formation of scar tissue in the navel region where most bites were inflicted.