How Do Insects Breathe?

This is how respiration works in insects.

Diving beetle larva.
Aquatic insects can breathe underwater. Getty Images/Oxford Scientific/Larry Crowhurst

Insects require oxygen to live and produce carbon dioxide as a waste product, just as humans. That is where the commonality between the insect and human respiratory systems essentially ends.

Insects do not have lungs, nor do they transport oxygen through their circulatory systems. Instead, the insect respiratory system relies on a simple gas exchange system to bathe the insect's body in oxygen and to expel carbon dioxide waste.

Insect Respiratory System

Air enters the respiratory systems of insects through a series of external openings called spiracles. These external openings, which act as muscular valves in some insects, lead to the internal respiratory system, a densely networked array of tubes called tracheae.

To simplify the insect respiratory system, it acts like a sponge. The sponge has small holes that let water into the sponge moistening the sponge. Similarly, the spiracle openings allow air into the interior tracheal system bathing the insect's tissues with oxygen. Carbon dioxide, a metabolic waste, exits the body through the spiracles.​

The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting muscles surrounding the spiracle. In order to open, the muscle relaxes. 

How Can Insects Control Respiration?

Insects can control respiration to some degree. An insect can open and close its spiracles using muscle contractions.

For example, an insect living in a dry, desert environment can keep its spiracle valves closed to prevent moisture loss.

Also, insects can pump muscles in their bodies to force air down the tracheal tubes, thus speeding up the delivery of oxygen. In cases of heat or stress, insects can even vent air by alternately opening different spiracles and using muscles to expand or contract their bodies.

Still, the rate of gas diffusion, or flooding the inner cavity with air, cannot be controlled. As long as insects breathe using the spiracle and tracheal system, they are not likely to get much larger than they are now.

How Do Aquatic Insects Breathe?

While oxygen is plentiful in air (200,000 parts per million in the air), it is considerably less accessible in water (15 parts per million in cool, flowing water). Despite this respiratory challenge, many insects live in water during some stages of their life cycles.

How do aquatic insects get the oxygen they require while submerged? To increase their oxygen uptake in water, all but the smallest aquatic insects employ innovative structures that can get oxygen in and carbon dioxide out—such as using gill systems and structures similar to human snorkels and scuba gear.

Insect Aquatic Gills

Many water-dwelling insects have tracheal gills, which are layered extensions of their bodies that enable them to take more oxygen from the water. These gills are most often located on the abdomen, but in some insects, they are found in odd and unexpected places. Some stoneflies, for example, have anal gills that look like a cluster of filaments extending from their hind ends.

Dragonfly nymphs have gills inside their rectums.

Hemoglobin Can Trap Oxygen

Hemoglobin can facilitate the capture of oxygen molecules from the water. Non-biting midge larvae from the Chironomidae family and a few other insect groups possess hemoglobin, much like vertebrates do. Chironomid larvae are often called bloodworms because the hemoglobin gives them a bright red color. Bloodworms can thrive in water with exceptionally low oxygen levels. They undulate their bodies in the muddy bottoms of lakes and ponds to saturate the hemoglobin with oxygen. When they stop moving, the hemoglobin releases oxygen, enabling them to breathe in even the most polluted aquatic environments. This backup oxygen supply may only last a few minutes, but it is usually long enough for the insect to move into more oxygenated water.

Snorkel System

Some aquatic insects, like rat-tailed maggots, maintain a connection with air on the surface through a snorkel-like structure. A few insects have modified spiracles that can pierce the submerged portions of aquatic plants, and take oxygen from air channels within their roots or stems.

Scuba Diving 

Certain aquatic beetles and true bugs can dive by carrying a temporary bubble of air with them, much like a SCUBA diver carries an air tank. Others, like riffle beetles, maintain a permanent film of air around the bodies. These aquatic insects are protected by a mesh-like network of hairs that repels water, providing them with a constant airspace from which to draw oxygen. This airspace structure, called a plastron, enables them to remain permanently submerged.

Sources:

  • The Insects: An Outline of Entomology, 3rd edition, by P.J. Gullan and P.S. Cranston
  • An Introduction to the Aquatic Insects of North America, by Richard W. Merritt and Kenneth W. Cummins.
  • "Respiration in Aquatic Insects," by John R. Meyer, Department of Entomology, North Carolina State University (2015).
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Hadley, Debbie. "How Do Insects Breathe?" ThoughtCo, Oct. 15, 2017, thoughtco.com/how-do-insects-breathe-1968478. Hadley, Debbie. (2017, October 15). How Do Insects Breathe? Retrieved from https://www.thoughtco.com/how-do-insects-breathe-1968478 Hadley, Debbie. "How Do Insects Breathe?" ThoughtCo. https://www.thoughtco.com/how-do-insects-breathe-1968478 (accessed December 14, 2017).