At insects living in water, breathing is carried out in two ways. It depends on what structure their tracheal system has.
Many of the aquatic organisms have a closed tracheal system in which the spiracles do not function. It is closed, and there are no “exits” to the outside in it. Breath It is carried out with the help of gills - outgrowths of the body, into which the trachea enter and branch abundantly. Thin tracheoles come so close to the surface of the gills that oxygen begins to diffuse through them. This allows some insects living in the water (larvae and nymphs of caddis flies, stoneflies, mayflies, dragonflies) to carry out gas exchange. During their transition to terrestrial existence (turning into adults), the gills are reduced, and the tracheal system from closed to open.
In other cases, the respiration of aquatic insects is carried out by atmospheric air. These insects have an open tracheal system. They take in air through the spiracles, floating to the surface, and then descend under the water until it is used up. In this regard, they have two structural features:
- firstly, developed air sacs, in which large portions of air can be stored,
- secondly, the developed locking mechanism of the spiracles, which does not let water into the tracheal system.
Other features are also possible. For example, in the larva of the swimming beetle, the spiracles are located at the posterior end of the body. When she needs to "take a breath", she swims to the surface, assumes a vertical position "upside down" and exposes the part where the stigmas are located.
In the larva of an ordinary mosquito, from the 8 and 9 segments of the abdomen connected together, a breathing tube extends up and back, at the end of which the main tracheal trunks open. When the tube is exposed above the water, the insect receives air through the gaps in the trunks. Almost the same, but more pronounced tube is found in Eristalis larvae. This formation is so pronounced in them that for its presence and the gray color of the insect itself, such larvae are called "rats". Depending on the stay at a greater or lesser depth, the tail of the "rat" can change its length. (a photo)
The breathing of adult swimmers is interesting. They have developed elytra, from the sides bending down and inward, towards the body. As a result, when floating to the surface with folded elytra, the beetle captures an air bubble that enters the subelytral space. The spiracles open there. Thus, the swimmer renews oxygen supplies. A swimmer of the genus Dyliscus can stay under water for 8 minutes between ascents, Hyphidrus for about 14 minutes, Hydroporus for up to half an hour. After the first frost under the ice, the beetles also retain their viability. They find air bubbles under the water and swim over them in such a way as to "take" them under the elytra.
In aquatic, the storage of air occurs between the hairs located on the abdominal part of the body. They are not wetted, so a supply of air is formed between them. When an insect swims under water, its ventral part appears silvery due to the air cushion.
In aquatic insects breathing atmospheric air, those small reserves of oxygen that they capture from the surface should be used up very quickly, but this does not happen. Why? The fact is that oxygen diffuses from the water into the air bubbles, and carbon dioxide partially escapes from them into the water. Thus, taking air under water, the insect receives a supply of oxygen, which replenishes itself for some time. The process is highly dependent on temperature. For example, the Plea bug can live in boiled water for 5-6 hours at warm temperatures and 3 days at cold temperatures.
Insects don't have lungs. Their main respiratory system is the trachea. Insect tracheae are communicating air tubes that open outward on the sides of the body with spiracles. The finest branches of the trachea - tracheoles - permeate the entire body, braiding organs and even penetrating inside some cells. Thus, oxygen is delivered with air directly to the place of its consumption in the cells of the body, and gas exchange is ensured without the participation of the circulatory system.
Many insects living in water (aquatic beetles and bugs, larvae and pupae of mosquitoes, etc.) must rise to the surface from time to time to capture air, i.e. they also breathe air. The larvae of mosquitoes, weevils and some other insects, for the time of renewal of the air supply in the tracheal system, are “suspended” from below to the surface film of water with the help of non-wettable greasy hairs.
And aquatic beetles - hydrophiles (Hydrophilidae), swimmers (Dytiscidae) and bugs, for example, smoothies (Notonectidae) - breathing near the surface, carry away an additional supply of air with them under the water under the elytra.
In insect larvae living in water, in moist soil and in plant tissues, skin respiration also plays an important role.
The larvae of mayflies, stoneflies, caddisflies and other insects, well adapted to life in water, do not have open spiracles. Oxygen in them penetrates through the surface of all parts of the body where the covers are thin enough, especially through the surface of leaf-shaped outgrowths pierced by a network of blindly ending tracheae. In larvae of mosquitoes (Chironomus), respiration is also cutaneous, with the entire surface of the body.
). On the sides of the body there are up to 10 pairs, sometimes less, of spiracles, or stigmas: they lie on the meso- and metathorax and on 8 segments of the abdomen.
The stigmas are often equipped with special closing devices and each lead into a short transverse canal, and all the transverse canals are connected to each other by a pair (or more) of the main longitudinal tracheal trunks. Thinner tracheas originate from the trunks, branching many times, and entangling all organs with their branches. Each trachea ends with a terminal cell with radially divergent processes pierced by the terminal tubules of the trachea (Fig. 341). The terminal branches of this cell (tracheoles) penetrate even into individual cells of the body.
Sometimes the tracheas form local expansions, or air sacs, which serve in terrestrial insects to improve air ventilation in the tracheal system, and in aquatic insects, probably as reservoirs that increase the air supply in the animal's body.
Tracheae arise in the embryo of insects in the form of deep protrusions of the ectoderm; like the rest of the ectodermal formations, they are lined with a cuticle (Fig. 341). In the surface layer of the latter, a spiral thickening is formed, which gives the trachea elasticity and prevents the walls from falling off.
In the simplest cases, oxygen enters the tracheal system and carbon dioxide is removed from it by diffusion through constantly open stigmas. This is observed, however, only in inactive insects living in conditions of high humidity.
The activation of behavior and the transition to living in arid biotopes significantly complicate the mechanism of respiration. The increasing need of the body for oxygen is provided by the appearance of special respiratory movements, consisting of relaxation and contraction of the abdomen. In this case, the tracheal sacs and the main tracheal trunks are ventilated. The formation of closing apparatuses on stigmas reduces the loss of water during respiration. Since the rate of diffusion of water vapor is lower than that of oxygen, when the stigmas are opened for a short time, oxygen has time to penetrate into the tracheal system, and water losses are minimal.
In many insect larvae living in water (for example, dragonflies, mayflies, etc.), the tracheal system is closed, that is, there are no stigmas, while the tracheal network itself is present. In such forms, oxygen diffuses from the water through the tracheal gills, lamellar or bushy, thin-walled outgrowths of the body, penetrated by a rich network of tracheae (Fig. 342). Most often, the tracheal gills sit on the sides of a part of the abdominal segments (mayfly larvae). Oxygen enters through the thin covers of the gills, enters the trachea and then spreads through the body.
During the transformation of the gill-breathing larvae into an adult insect living on land, the gills disappear, and the stigmas open and the tracheal system changes from closed to open.
An important physiological feature of the respiratory system of insects is as follows. Ordinarily, oxygen is perceived by an animal in certain parts of its body and from there it is carried by the blood throughout the body. In insects, the air tubes permeate the entire body and deliver oxygen directly to the places of its consumption, i.e., to tissues and cells, as if replacing blood vessels.
How do insects breathe, and do they breathe at all? The body structure of the same beetles differs significantly from the anatomy of any mammal. Not all people know about the features of the life of insects, because it is difficult to observe these processes due to the small size of the object itself. However, these questions sometimes come up - for example, when a child puts a captured beetle in a jar and asks how to ensure a long, happy life for him.
So do they breathe, how is the process of breathing carried out? Is it possible to close the jar tightly so that the bug does not run away, will it suffocate? These questions are asked by many people.
Oxygen, respiration and insect size
Modern insects are really small in size. But these are exceptionally ancient creatures that appeared much earlier than warm-blooded ones, even before dinosaurs. In those days, the conditions on the planet were completely different, the composition of the atmosphere was also different. It's even amazing how they could survive millions of years, adapt to all the changes that have taken place during this time on the planet. The heyday of insects is behind, and in those days when they were at the peak of evolution, it was impossible to call them small.
Interesting fact: the fossilized remains of dragonflies prove that in the past they reached half a meter in size. During the heyday of insects, there were other exceptionally large species.
In the modern world, insects cannot reach this size, and the largest are tropical individuals - a humid, hot, oxygenated climate gives them more opportunities to thrive. Literally all researchers are convinced that it is precisely their respiratory system with its specific device features that prevents insects from flourishing on the planet in today's conditions, as it was in the past.
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Respiratory system of insects
When classifying insects, they are classified as a subtype of tracheal breathing. This already answers many questions. Firstly, they breathe, and secondly, they do this through the trachea. Arthropods are also classified as gill-breathers and chelicerae, the former being crayfish and the latter being mites and scorpions. However, let us return to the tracheal system, characteristic of beetles, butterflies, and dragonflies. Their tracheal system is extremely complex; evolution has polished it for more than one million years. The tracheae are subdivided into numerous tubes, each tube goes to a certain part of the body - in much the same way as the blood vessels and capillaries of more advanced warm-blooded, and even reptiles, diverge throughout the body.
The tracheae fill with air, but this is not done through the nostrils or mouth, as in vertebrates. The trachea are filled with spiracles, these are the numerous holes that are on the body of the insect. Special valves are responsible for air exchange, filling these holes with air, and closing them. Each spiracle is supplied by three branches of the trachea, including:
- Ventral for the nervous system and abdominal muscles,
- Dorsal for dorsal muscles and spinal vessel, which is filled with hemolymph,
- Visceral, which works on the organs of reproduction and digestion.
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The tracheae at their end turn into tracheoles - very thin tubes that braid each cell of the insect's body, providing it with an influx of oxygen. The thickness of the tracheol does not exceed 1 micrometer. This is how the respiratory system of an insect is arranged, due to which oxygen can circulate in its body, reaching every cell.
But only crawling or low-flying insects have such a primitive device. Flyers, such as bees, also have air sacs like those of birds in addition to lungs. They are located along the tracheal trunks, during flight they are able to contract and inflate again in order to provide maximum air flow to each of the cells. In addition, waterfowl insects have systems for retaining air on the body or under the abdomen in the form of bubbles - this is true for swimming beetles, silverfish, and others.
How do insect larvae breathe?
Most larvae are born with spiracles; this is true primarily for insects living on the surface of the earth. Aquatic larvae have gills that allow them to breathe underwater. Tracheal gills can be located both on the surface of the body and inside it - even in the intestines. In addition, many larvae are able to receive oxygen throughout the surface of their body.
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