(1) In a shallow cool temperate pond Diptera of the families Tipulidae and Stratiomyiidae were the major faunal components. All species except one had a single, well synchronized adult emergence period within the interval May-October. The mean dates of first and last emergence were 26 June and 7 August, giving a mean emergence period of 42 days. (2) Using Cluster analyses of matrices of coefficients of association, seven faunal elements, each exhibiting a different distribution pattern in four defined areas of the pond, were identified. The main sediment variables which influenced larval distributions were particle size, organic content and carbon/nitrogen ratio. A flocculent high organic content sediment contained a more diverse fauna than a compacted low organic sediment. (3) In the larvae of all non-predatory species examined allochthonous vascular plant material was the dominant food component. However, feeding studies on Stratiomys barbata indicated that such material alone was not a nutritious food source and that the presence of attached micro-organisms was necessary for growth. (4) In the pond three major functional feeding groups were recognized, namely shredders, collectors and predators. The shredders reduce the size of organiz particles and make available to the collectors the small particles on which they feed (Cummins 1973). No marked seasonal or between-instar changes were observed in the food of a selected shredder (Ptychoptera lenis) and a selected collector (Stratiomys barbata), but differences in minor food components proved to be a good indicator of the animals functional group.
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