In addition to the four major categories listed above, insects also acquire water, vitamins, and minerals from their food. Most terrestrial insects are highly-adapted for water conservation and get most of the water they need directly from their food. A drop of morning dew is usually sufficient for the few insects who actively drink water. Insects like flour moths and grain beetles survive on surprisingly small amounts of water. Some species can live for months on only the “metabolic” water they generate as a byproduct of protein synthesis or chitin synthesis. These chemical reactions free a single molecule of water each time a simple sugar is added to a polysaccharide (or an amino acid is added to a protein).
Vitamins include a number of complex organic molecules that animals need in very small amounts for specialized metabolic processes. (Coenzyme A, for example, is made from pantothenic acid). Humans (and most other mammals) must have a dietary source of both fat-soluble and water-soluble vitamins to ensure good health. Insects, however, have the ability to synthesize their own fat-soluble vitamins (A, D, E, and K) from other compounds. They still need a dietary source of most water-soluble vitamins such as thiamine (B1), riboflavin (B2), pyridoxine (B6), nicotinic acid, pantothenic acid, ascorbic acid (C), and biotin (H).
Minerals are inorganic substances that animals also need in relatively small amounts. Iron and copper atoms are needed for cytochromes; nerves and muscles need calcium, sodium, and potassium ions; phosphorus is a component of cell membranes; and sulfur atoms play a significant role in both three-dimensional structure of proteins and sclerotization of the exoskeleton.