Mosquito larvae are aquatic, but have never adapted to breathing underwater. Instead, mosquito larvae must come to the surface of the water to breathe oxygen. Mosquito larvae have an extensions of their hindgut called anal papillae. The anal papillae form a tube that protrudes above the surface of the water when creating. Hairs at the end of the tube lay on the surface of water where they repel and prevent water from entering the tube.
The anal papillae have another function, absorption of salts from dilute fresh water. The salt concentration within a mosquito larva is higher than the salt concentration in fresh water. The anal papillae are involved in transporting salts against a concentration gradient. The anal papillae exchange protons and waste ammonia for other cations that are necessary for mosquito growth and development.