TRACHEAL RESPIRATION: CHARACTERISTICS AND EXAMPLES OF ANIMALS - BIOLOGY - 2025

The tracheal breathing is the most commonly used type breathing by insects centipedes, ticks, spiders and parasites. In these insects, respiratory pigments are absent from the blood, as the tracheal system is responsible for distributing O2 (air) directly to the cells of the body.

Tracheal respiration allows the process of gas exchange to take place. In this way, a series of tubes or tracheae are strategically located in the body of the insects. Each of these tracheas has an opening towards the outside that allows the entry and exit of gases.

Spiracles and tracheal system

As in vertebrate animals, the process of expelling gases from the body of insects depends on the muscular contraction movement that presses on all the internal organs of the body, forcing CO2 out of the body.

This type of respiration occurs in most insects, including those that inhabit aquatic environments. This type of insects has bodies specially prepared to be able to breathe while they are submerged below the water level.

Parts of the tracheal breathing system

Windpipe

The trachea is a widely branched system with small ducts that air passes through. This system is located throughout the entire body of insects.

The presence of ducts in it is possible thanks to the existence of body walls internally aligned by a membrane known as the ectoderm.

An insect has several tracheas or ducts that open to the outside of its body, allowing the process of gas exchange to take place directly in all the cells of the insect's body.

The area where there is a greater concentration of branches is usually the belly of the insect, which has numerous ducts that progressively give way to the air inside the body.

The complete tracheal system of an insect is generally made up of three main channels located parallel and longitudinally in relation to its body. Other small ducts pass through the main tracheas, forming a network of tubes that encompasses the entire body of the insect.

Each of the tubes that has an outlet to the outside, ends in a cell called a tracheal cell.

In this cell, the tracheae are lined with a layer of protein known as trachein. In this way, the outer end of each trachea is filled with tracheolar fluid.

Spiracles

Scanning electron microscope image of a cricket blowhole valve.

Source: user chsh CC BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5)

The tracheal system opens to the outside through slit openings called stigmas or spiracles. In cockroaches, there are two pairs of spiracles located in the thoracic region and eight pairs of spiracles located in the first segment of the abdominal region.

Actias selene, Source: user Kugamazog ~ commonswiki CC BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5)

Each blowhole is surrounded by a sclerite called peritrema and has bristles that act as filters, preventing dust and other particles from entering the tracheae.

The spiracles are also protected by valves attached to the occluder and dilator muscles that regulate the opening of each tube.

Gas exchange

In a resting state, the tracheae are filled by capillary fluid thanks to the low osmotic pressure in the cells of the body tissue. In this way, the oxygen entering the ducts dissolves in the tracheolar fluid and the CO2 is released into the air.

Tracheolar fluid is absorbed by the tissue when the volume of lactate increases once the insect enters the flight phase. In this way, the CO2 is temporarily stored as bicarbonate, sending signals to the spiracles to open.

However, the greatest amount of CO2 is released through a membrane known as the cuticle.

Ventilation movement

Ventilation of the tracheal system takes place when the muscular walls of the insect's body contract.

The expiration of gas from the body occurs when the back-abdominal muscles contract. On the contrary, the inspiration of air happens when the body takes its regular shape.

Insects and some other invertebrates carry out gas exchange by removing CO2 through their tissues and taking in air through tubes called tracheae.

In crickets and grasshoppers, the first and third segments of their thorax have a blowhole on each side. Similarly, eight other pairs of spiracles are located linearly on each side of the abdomen.

Smaller or less active insects carry out the process of gas exchange by diffusion. However, insects that breathe through diffusion can suffer in drier climates, since water vapor is not abundant in the environment and will not be able to diffuse into the body.

Fruit flies avoid the risk of dying in dry environments by controlling the size of the opening of their blowholes in such a way that they adapt to the oxygen needs of the muscles during the flight stage.

When the demand for oxygen is lower, the fruit fly partially closes its spiracles in order to retain more water in the body.

The most active insects such as crickets or grasshoppers, must constantly ventilate their tracheal system. In this way, they must contract the muscles of the abdomen and press the internal organs to force the air out of the windpipes.

Grasshoppers have large air sacs attached to certain sections of the larger tracheae, in order to increase the effectiveness of the gas exchange process.

Aquatic insects: example of tracheal respiration

Aquatic larva of the Aedes aegypti mosquito. Taken and edited from: Econt

Aquatic insects use tracheal respiration to carry out the process of gas exchange.

Some, like mosquito larvae, take in air by exposing a small breathing tube above the water level, which is connected to their tracheal system.

Some insects that can soak in water for long periods of time carry air bubbles from which they take the O2 they need to survive.

On the other hand, some other insects have spiracles located on the upper part of their back. In this way, they pierce the leaves that are suspended in the water and adhere to them in order to breathe.

References

1. biology-pages. (January 24, 2015). Obtained from Tracheal Breathing: biology-pages.info.
2. Site, TO (2017). Part III: How Living Organisms Breathe: Index. Obtained from THE BREATHING SYSTEM OF INSECTS: saburchill.com.
3. Society, TA (2017). Amateur Entologists' Society. Obtained from Insect respiration: amentsoc.org.
4. Spider, W. (2003). Insects and Spiders of the World, Volume 10. New York: Marshall Cavendish.
5. Stidworthy, J. (1989). Shooting Star Press.
6. Yadav, M. (2003). Biology Of Insects. New Delhi: DPH.
7. Yadav, M. (2003). Physiology of Insects. New Delhi: DPH.