Insects (insects) are a general term for arthropods classified in the Hexapoda subphylum Insects (scientific name: Insecta). It is also collectively called insects, but it is sometimes used to mean hexapods including insects and entognatha.
In the past, all hexapods were included in insects, but the classification system has been revised, and now the classification group of Entognatha (Entognatha) (Springtail, Protura, Diplura) is excluded. These are also mentioned in this section.
Insects are a group of diverse arthropods that have evolved especially on land.
Most species live on land, some in freshwater, with the exception of those in the sea. Insects that live in water are called aquatic insects (aquatic insects), and are thought to have been secondarily adapted to underwater life from their ancestors that evolved on land. It is adapted to the climate and environment of the earth and has a very high species diversity.
According to the National Museum of Nature and Science in Japan, there are about 1 million known insect species as of 2018, accounting for more than half of the confirmed species. It is estimated that there are many undiscovered and unclassified insects.
Although it is a group of animals commonly known as "insects", it is not a name that specializes in insects, but is a miscellaneous general term that includes many small animals other than insects such as pill bugs, spiders, centipedes, earthworms, and snails. ..
The following are general characteristics of insects. However, some parasitic insects and some larvae deviate significantly from these characteristics.
Like other arthropods, the body of an insect is made up of repeating structures of somites called somites. In insects, there are three sets of body segments: the head containing the first and immediate 5 segments, the chest containing the 3 segments (thorax), and the abdomen containing the 11 segments (abdomen). It is organized in a tagma. The somites of the head are completely fused into one structure, and the abdomen appears to be less than 10 somites because the final somites are degenerative.
As a general rule, the appendages (arthropods) and other appendages of each part have a pair of antennae, mandibles, and maxillas on the head, and the upper lip (labrum) and lower part in the anterior-posterior direction. There is one labium each, three pairs of legs on the chest, two pairs of gonopods and one pair of cerci on the abdomen. The lower lip is the fused second maxilla, and the gonopod is often a remarkably specialized genital organ with a morphology that does not resemble an appendage.
The respiratory system is the tracheal system, which opens the spiracles on both sides of the chest and abdomen. Aquatic insects may have other respiratory organs such as gills in the abdomen.
Most insects (winged insects) have two pairs of wings on their chest and can fly in the sky. The first animals to fly in the sky are said to be insects. The structure of the insect wings varies from group to group and corresponds to the breadth of their lives.
Special sensory organs include the eyes and antennae. It has small receptors in each other part.
Most insects have a pair of arthropods and three or less monoculars on their heads. If you have both, if you have only one, there are cases where you do not have both in a small part. The arthropod acts as the main visual organ, and well-developed ones are considered to have excellent vision. It also has the ability to see ultraviolet light. That is, anatomically, there are cells that sense ultraviolet rays in the eyes of insects. Even insects that cannot distinguish between male and female colors with the human eye (for example, the color of the wing of the cabbage white butterfly).