Behaviour and local distribution of the freshwater oligochaete Nais pardalis Piguet (Fam. Naididae)

1. Nais pardalis Piguet, a small freshwater oligochaete, lives in the surface few cm of sandy sediments in Loch Leven, County of Kinross, Scotland. 2. It forms branching passageways or tubes in the sediment not by any active constructional behaviour, but by the secretion of a material which sticks the sand grains together. 3. The sand grains making up the tubes are exactly the same size as those in the surrounding sediment. 4. Animals select the smallest grains in their environment for ingestion. 5 In the laboratory, rates of ingestion of sand grains measured on different animals vary from 5 to 60 grains/hour and rates of excretion from 3 to 6/hour, but these figures should be viewed with caution. 6. Analysis of the rate of ingestion of sand grains indicates that grains are not ingested randomly in time. Having eaten one grain, an animal is less likely to eat another within the next 10 seconds.