One method of removing incoming excess water is the ample production of urine, in many cases this is also combined with amounts of ammonia. Salt reabsorbtion also occurs in the gut and Na and Cl ions are known to be reabsorbed by an active uptake process within the rectum. Certain larvae are able to uptake salts from very dilute solutions using active processes. This can be seen in Aedes , Culex and Chironomus which use anal papillae as the uptake site. Larval uptake of salts from such dilute solutions maybe due to their increased loss through their permeable cuticle.
Many larvae lack the lipid layer seen in the adults.
Chloride epithelia are used for ion uptake in Odonata and Diptera. These are localised areas of integument which actively take up and replace ions from the surrounding water. Aquatic insects of marine habitats have to deal with extreme osmotic pressures. This adaptation has allowed them to exploit a niche within salt pans which have huge fluctuations in salinity. Neuston insects live on the surface tension of water.