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Arthropods (continued)


They are arthropods with six paws distributed in three pairs connected to the chest. Insects have a subdivided body head, chest and abdomen. They have a pair of antennae, two pairs of wings, most of the time, but there are species with only one pair and others without wings.

Metamers are unequal in size and during embryonic development some of them may fuse together. This fusion happens in the formation of the head, resulting in a small piece. In it the mouth is ventral and surrounded by pairs of buccal parts of chewing function and other articulated appendages, modified for grasping the food, the so-called maxillary palpates.

On the head are still a pair of articulated antennas (of sensory function) and, laterally, two spots corresponding to the eyes. They are eyes composed of several hexagonal units known as ommatids, responsible for the image composition of objects seen by insects.

Insect Digestive System

Didactically, we can distinguish three portions of the digestive tract: anterior, middle and posterior. The anterior and posterior portions are internally coated with chitin. The anterior portion is mainly responsible for the mechanical treatment of food, although there may be action of digestive enzymes produced in the middle portion. It is in the middle portion that happens the chemical digestion, from enzymes coming from its walls or from plaques formed in this region. The posterior portion is responsible for water reabsorption and stool elaboration.

In the mouth, there are two salivary glands whose secretion begins the process of chemical digestion. Also noteworthy is the thin-walled gut and a thick-walled gizzard in the digestive tract. In the crop occurs the action of various digestive enzymes and in the gizzard is the grinding of food.

Next, the food is taken to the intestine, where there are some blind-bottomed tubular projections, the caeca. At these two sites, chemical digestion proceeds and absorption of the digested food is sent to the blood.

Insect excretory system

The Malpighi Tubules They are located at the border between the middle portion and the posterior portion of the intestine. Each tubule has a blind bottom and plunges into the body's gaps, from which it removes impurities and discharges them into the intestines for elimination with feces.

The nitrogen excretion product of insects is the uric acid, a substance that requires very little water for its elimination (another important factor in the adaptation of insects to the terrestrial environment).

Insect circulatory system

In most insects, "blood" is colorless and called hemolymph. The circulation is of the lacunar or open type. The heart is dorsal and pumps the hemolymph to the anterior extremity, causing it to reach body gaps or hemocells where the changes (nutrients in excreta) in the tissues slowly occur. In insects, gas exchange in respiration is not done by the circulatory system. The hemolymph returns to the heart through small lateral holes (ostia) in the walls of the organ.

Insect Respiratory System

Insects breathe through tracheas, small channels that connect cells inside the body with the environment. Each tracheal tubule branches and generates increasingly thin tubules that penetrate cells, oxygenating them and removing carbon dioxide as a product of respiration. Contraction movement of the abdominal muscles continually renew the air of the trachea, similar to a bellows.

Insect breeding system

Insects have separate sexes and their fertilization is internal. They are oviparous animals, which can have three types of development:

  • Directwithout metamorphosis: developed metabolo (a = without, metabolo = change). Ex .: bookworm. From the egg hatches a young similar to the adult.
  • Indirectwith gradual or incomplete metamorphosis: hemimetabol development (hemi = medium). Eg grasshopper, cockroach, thumbtack. From the egg hatches a form called a nymph, which is similar to an adult (or imago) but has no developed wings.

  • Indirect, complete metamorphosis: holometable development (holo = total). Exs: Butterflies, flies and fleas. From the egg hatches a larva, also called a caterpillar, quite distinct from the adult. This larva goes through an actively feeding period, and then enters the stage called pupa when metamorphosis occurs: the larva becomes the fully formed adult or imago. Larvae of some butterfly or moth species produce a cocoon that protects the pupa. Once an adult, the holometabolo insect no longer grows and therefore no longer grows. The larval phase can last from months to over a year, and the adult phase can last from a week to a few months. The duration of these phases depends on the species.

Some holometabolic insects have aquatic larval phase, as is the case with important disease-bearing mosquitoes. Eg Culex, which transmits elephantiasis, Anopheles, which transmits malaria, Aedes aegypti, which transmits dengue fever and yellow fever.