Drainage ditches are a familiar and common habitat in the Netherlands. Until recently however they have been the focus of few ecological studies. Extensive studies on Walcheren, a brackish water region of The Netherlands, have shown that chironomid larvae form a major component of the animal communities in the mud. The spatial distribution of some of these species can be correlated with the chloride concentration of the water. Biometric data are included for the speciesChironomus salinarius, C. halophilus andC. plumosus.