Sentence:  Cattle were grazing languidly on the lush grass and flicking their tails to keep away the <WSD>clegs</WSD> that constantly plagued them and, having recently suffered a nasty bite from one, I was wary of them myself. 
Meaning of the word marked with <WSD> tags:  A blood-sucking fly of the family (Tabanidae); a gadfly, a horsefly.