The Copepoda not only form the greatest part of the pelagic life in temperate seas, but are also of the greatest importance in pelagic economy. Feeding on minute organisms and particles of animal and vegetable matter, they are themselves a prey to larger organisms. Some fishes such as the herring, pilchard, and mackerel feed almost exclusively on Copepoda at certain seasons of the year, and experienced fishermen are accustomed to look on the swarms of Copepods which make their appearance in the spring and early summer as the sure precursors of a shoal of fish.