How Do Insects Breathe?

How Respiration Work 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 we do. To say insects breathe, though, might be a stretch. They don't have lungs, nor do they transport oxygen through their circulatory systems. Instead, insects use a series of tubes called a tracheal system to perform gas exchange throughout the body.

Gas Exchange Through Simple Diffusion

Gas exchange, or what we think of as breathing, is accomplished mostly by simple diffusion through the cell walls.

Air enters the spiracles, and moves through the tracheal system. Each tracheal tube ends in a moist tracheole, a specialized cell for exchanging gases with another cell in the body.

When air reaches the tracheole, oxygen dissolves into the tracheole liquid. Through simple diffusion, oxygen then moves to the living cell and carbon dioxide enters the tracheal tube. Carbon dioxide, a metabolic waste, exits the body through the spiracles.

This explains the movement of gases, but can insects control their respiration? Yes, to some degree. The insect opens and closes the spiracles using muscle contractions. An insect living in a dry, desert environment will keep the spiracle valves closed to prevent moisture loss. Insects can also pump muscles throughout their bodies to force air down the tracheal tubes, thus speeding up the delivery of oxygen. In heat or under stress, insects can even vent air by alternately opening different spiracles and using muscles to expand or contract their bodies.

Still, diffusion places some limits on the insect body. The rate of gas diffusion cannot be controlled, and only proves efficient for small organisms. This limiting factor probably benefits us, as otherwise we might find ourselves living with giant-sized insects! As long as insects breathe using simple diffusion, they aren't likely to get much larger than they are now.

How Do Aquatic Insects Breathe?

While oxygen is plentiful in air (O2 levels in air are 200,000 parts per million), it is considerably less accessible in water (reaching just 15 ppm in cool, flowing water). Despite this respiratory challenge, many insects live in water during some stages of their life cycles. So 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 structures that effectively increase the surface area available for gas exchange.

Many water-dwelling insects have tracheal gills, layered extensions of their bodies that enable them to take more oxygen from the water than they could otherwise. These gills are most often located on the abdomen, but in some insects they're 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.

A few aquatic invertebrates use respiratory pigments to extract oxygen from water. Non-biting midge larvae (family Chironomidae) and a few other insect groups possess hemoglobins, much like vertebrates do. Chironomid larvae are often called bloodworms, because the hemoglobin gives them a bright red color.

Bloodworms can thrive even in water with exceptionally low oxygen levels. They undulate their bodies in the muddy bottoms of lakes and ponds to saturate their hemoglobins with oxygen. When they stop moving, the hemoglobins release the oxygen, enabling them to breathe in even the most polluted aquatic environments.

Some insects that inhabit aquatic environments still get their oxygen from the air, using an open tracheal system like terrestrial insects. Some of these aquatic insects, like rat-tailed maggots, maintain a connection with air on the surface through a snorkel-like structure. A few remarkable insects have modified spiracles that can pierce the submerged portions of aquatic plants, and take oxygen from air channels within their roots or stems.  

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 setae (hairs) that repels water, providing them with a constant airspace from which to draw oxygen. This 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. Accessed online March 17, 2016.