Observations on the ecology of Simuliidae from the River Frome, Dorset

Abstract. 1. The species of Simulium present at twenty‐seven stations in the River Frome and some of its tributaries are recorded. 2. In the lower reaches of the river Simulium omatum and Simulium lineatum have basic life histories comprising four generations of larvae annually. 3. At other stations the annual pattern is modified by weed cutting and flow regulations and by position in the river system. 4. In winter generations the larvae and pupae are larger than at other times of the year. A survey of the size of pupae at ten stations in October 1973 indicated that temperature could account for variations in size.