Water economy of the earthworm Lumbricus terrestris L.: Coping with the terrestrial environment

Although it displays many characteristics of a freshwater ani‐mal, the earthworm Lumbricus terrestris survives well in moist terrestrial environments. Earthworms in soil are only partially hydrated and gain weight when transferred to pond water. Worms in air of 70–80% relative humidity (RH) have a much higher dehydration rate than do animals at 100% RH. Compared with animals at 100% RH, the integumental water exchange rate of worms at 70–80% RH is significantly lower than expected based on the amount of water in the atmosphere. Lumbricus may reduce its integumental permeability to re‐strict water loss in terrestrial environments, but cannot regulate the osmotic pressure of its coelomic fluid at relative humidities lower than 100%.