Insects appeared on the earth about 350 million years ago and experienced a long evolution. Arthropods originated from worms similar to annelids and went through the following evolutionary stages:

(1) There are appendages for walking on the ventral side of each segment;

(2) Antennas, eyes and mouthparts occur in the head, and the head becomes the center of sensation and feeding;

③ The wings and feet are concentrated in the chest to become the action center; The abdomen is the center of internal organs and reproduction.

There are many theories about the origin of insects. One theory holds that insects evolved from aquatic ancestors, such as trilobites and crustaceans. Another theory holds that the origin of terrestrial ancestors, such as Polypoda, Lipopod and Synthetic, is close relatives of insects.