Chironomid midge larvae can saturate their haemoglobins through undulating their bodies within their silken tubes or substrate burrows to permit oxygenated water to flow over the cuticle. Oxygen is unloaded when undulations stop, or when recovery from anaerobic respiration is needed. The respiratory pigments allow a much more rapid oxygen release than is available by diffusion alone. Mechanisms that aid chironomids in withstanding the effects of pollution inculde a higher oxygen storage capacity because of the presence of haemoglobin and an ability to avoid heavy metals by burrowing into the sediment.