ABSTRACT
Several species of insects and mites present a particular challenge in the field of water transport: they are able to maintain the high water activity of their body fluids by active resorption of water vapor from substantially subsaturated atmospheres. The water-vapor uptake is performed by distinct but rather different organs at either end of the alimentary canal. In Tenebrionidae, the “cryptonephridial complex”, an association of rectal tissue and the distal parts of the Malpighian tubules, dehydrates the feces and absorbs water vapor from the air. For iso-osmotic water transport against negligible gradients, this form of electro-osmosis will be rather ineffective because of poor impedance matching. A. E. Hill and McLaughlin and R. T. Mathias propose the “classical” form of electro-osmosis for isotonic water transport. The hygroscopic phase is stationary in the cockroach Arenivaga and in most “anal absorbers”; energy must be spent to transfer the condensed water against the difference of its chemical potential into the hemolymph.
