What Are Spiracles in Biology?

Various species carry different body parts that help in breathing. One such is the Spiracles, the opening of the tracheal system located on the integument of the insect. 

These are basically breathing openings found on the surface of various insects, including sharks and stingrays. In fish, spiracles are composed of a pair that opens behind the eyes allowing drawing oxygenated water in without being gills to action. Once you understand the spiracle meaning, it becomes easy to study the breathing pattern of insects and animals.

In many cases of Apterygota and larval insects, there is a lack of valves in spiracles, therefore they have trachea that stays open, although they are covered with sieve-like plates.

Spiracles Definition

In some animal species, there is an opening on the surface of their skin, leading to the respiratory systems. Insects sometimes have it on the exoskeletons allowing air to enter the area called trachea. One can locate them laterally along the thorax, and in some insects it is found in the abdomen.

Small muscles operate one or two flap-like valves within each spiracle, relaxing to open it, and regulate the airflow.

One interesting point is the timing and duration of spiracle closures affecting respiratory rates of the organism. In many cases, these are surrounded by the hair helping to minimize the bulk air movement. This results in the minimizing of the water loss.

As mentioned above, different spices have different pairs of spiracles, like an adult can have at least 10. Similarly, the number of spiracles in cockroaches is 10, out of these 2 pairs are found in the thoracic portion and 8 are found in the abdominal portion.

These spiracles in many insects are protected by hairs and valves with flaps, and are surrounded by spines, folds and ridges. Further, spiracles are controlled by muscles which open up when in need of oxygen. During the resting period, these spiracles rest. One of the interesting things about spiracles is they can be adjusted in insects that can survive in dry climates.

The closing mechanism of the spiracle, or valve, carries enough protein required by the insect and is known as Resilin, allowing contraction and expansion.

Some Examples of Spiracles

From grasshopper spiracles to sharks, spiracles in insects and fish are found in different forms. There are different types of spiracles in insects you will come across. Southern stingrays, also known as sand-dwelling sea animals, use spiracles to breathe while lying on the ocean bottom. Skates and Cartilaginous fish carry flat bodies and wing-like pectoral fins attached to their heads.

Angel sharks, on the other hand, carry a flat body helping to bury themselves in the sand breath using spiracles. They lie beneath the sand, to wait and attack fish, crustaceans and other fish. Angel sharks absorb oxygen and eliminate carbon dioxide, and don’t have to swim like other sharks.

The spiracle leads to the trachea, which is also called the air tube.

Tracheal System in Insects

Insects don't carry any respiratory system. Instead, they carry a tracheal system delivering oxygen throughout their bodies, and removing carbon dioxide during respiration. As the air flows from the spiracle to the tracheal tube, it leads to the tracheoles, which are special cells used for the exchange of gas. Grasshopper spiracles are quite similar to the same as mentioned above. However, they need more pumping action, and help them when they are active or undergoing stress due to heat.

Insects of large size, open and close separate spiracles using abdominal muscles. This helps them to move air throughout their bodies. One of the reasons behind these insects aren’t evolving is because of the nature of these tubes.

Spiracles in Cockroaches

When you study the anatomy of cockroaches, there are 10 spiracles in cockroaches. These different numbers of spiracles in cockroaches are located in different areas. Some are found on thorax and parts of the legs. Rests are found in abdominal areas. The largest spiracle found in cockroaches is the first thoracic spiracle.

Types of Spiracles

There are different types of spiracles in insects and other animals. To identify them, you need to first know the spiracles definition.

1. Insects with Spiracles

There are different types of insects like cockroaches and grasshoppers which carry spiracles in different forms. Insects having spiracles allow air to move their tracheal system. Since insects don't carry lungs, they use the tracheal system for breathing purposes. Moreover, insect open and close spiracles with the use of muscle contraction. During this process, oxygen molecules travel through the insect's tracheal system.

2. Animal with Spiracles

Whales and sharks are some of the animals carrying spiracles for breathing purposes. Whales use blowholes to breathe in air and breathe out carbon dioxide.

All living things have different structures. Therefore, the organs present in them are also different, such as the respiratory system. Human beings and animals such as cows, birds, snakes, lions, and elephants have lungs as their primary respiratory system. Earthworms respire through their skin, Fishes respire through the gills and insects breathe through the spiral.

Introduction to Spiracles

Spiracles are openings found on the surface of certain cartilage fish such as insects, certain types of sharks and stingrays which lead to their respiratory system. In the case of fish, the spiracles of aquatic organisms consist of two openings just behind the eyes of the fish, allowing oxygen-rich water to be drawn in from above through the gills. The spiracles open into the mouth of the fish, where water passes through the gills and out of the body for gas exchange. Spirals help the fish breathe, even when the fish is lying on the ocean floor or buried in the sand.

Evolution of Spiracles 

In early jawless fish, spiracles were merely a gill opening behind the mouth. This gill opening eventually separated as the jaw evolved from the structure between it and the other gill openings. In most cartilaginous fish, the stigma remained as a small hole-like opening. The spiracles can breathe without the help of exposed gills, which helps with the types of rays buried in the ocean floor. So, it is likely the spiracle may have evolved from the opening of the gills. 

Animals with Spiracles 

Insects such as cockroaches have spiracles, small openings on their body that allow air to enter the tracheal system. Since insects do not have lungs, they use spiracles that open and close by the contraction of their muscles to exchange oxygen and carbon dioxide with the outside air. Oxygen molecules then move through the insect's tracheal system. Each tracheal tube ends in the trachea, where oxygen dissolves in the tracheal fluid. After that, oxygen diffuses into the cell. 

Spiracles in Insects 

Insects such as grasshoppers, cockroaches, houseflies, and mosquitoes breathe through the tracheal system. A network of tubes that make up the whole body of an insect. This trachea opens outward through tiny holes called the spiracles on either side of a part of the body. Each spiracle connects to a hole, the so-called tracheal tube, from which branches emerge and air enters the body. The trachea, a small branch of the trachea, reaches all cells in the body and supplies oxygen directly to all cells.