The object of this survey has been to investigate various aspects of the biology of the midge Chironomus zealandicus with a view to understanding certain phenomena arising from observations on the Christchurch Drainage Board's oxidation ponds. These include the larval rate of development at various water temperatures, the relationship between the chemical nature of the pond substratum and the distribution of the Chironomus larvae, and the osmo-regulatory limits of the two larval phenotypes (“thummi” phenotype possessing two pairs of ventral tubuli on the penultimate segment and the “salinarius” phenotype lacking these tubuli). For comparative purposes the Templeton and Auckland (Mangere) Sewage Treatment Works were included in the study. Between October 1962 and February 1963, complaints of midge infestation from adjacent residents prompted the Christchurch Drainage Board to introduce a midge sampling programme on the recently initiated oxidation ponds at Bromley. Craig and Burns published a report of the initial survey in March 1963 but since then nothing further has been published concerning observations on these ponds. Comparable surveys were instigated in Auckland (Spiller, 1964) and in the Western U, S. A. especially in California (Anderson et al. 1962, 1964). This survey began in November 1964, although preparatory investigations were carried out during a period of employment on midge control between December 1963 and April 1964.