Factors influencing the distribution and feeding of the larvae of Chironomus riparius

Chironomids are the most widely distributed group of insect larvae in fresh water environments. They are frequently the dominant primary consumers and show competitive interactions due to their requirements for foraging space in suitable substrates. In order to investigate the factors involved in sub strate selection a simple choice chamber has been constructed that enables larvae of Chironomus riparius Meigen (Diptera, Chironomidae) to select well s, in which they can establish tubes, according to a number of chemical and physical parameters. The statistical probabilities of them aggregating ran domly in this way were calculated for a variety of occupancies. The larvae developed distinct patterns of non-random aggregation in the wells. Subsequ ent experiments showed that the presence of food at sites of burrowing affe cted settling but physical irregularities were necessary in order to facili tate burrowing and establish random patterns. Once the animals had selected their habitat the rate of feeding on the sediment was relatively constant with a gut-clearance time of about 12 h although starving the animals befor e or after feeding affected the rate of passage of sediment through the ant erior of the gut.