Again, maintaining an osmotic balance is important to survival of organisms. The situation for aquatic insects is easy to apprehend. Insects living in fresh water are generally hyperosmotic to their environment. Under this condition water tends to diffuse into aquatic insects. If left unattended this process would effectively place cells in a very dilute environment.
Insects living in salt water, such as brine flies, are generally hypoosmotic to their environment.
These insects tend to lose water to the environment. Again, if left unattended, this would put the cells within the insect in a state of water loss and shrinkage. Equipped with a feeling for the nature of the problem, let us begin with a consideration of fresh water insects. The hemolymph, or extracellular compartment, of these insects is hyperosmotic to the water comprising their habitats. Water tends to pass through the cuticle and into insects.