JANUARY
2003

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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Check out these books by Tom Turpin:

Flies in the face of fashion

What's Buggin You Now?

 

 

 

1-23-03

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Insect Breathing Not Dependent on Noses


Animals need oxygen to live. The process is called respiration. Oxygen must get to cells within the animal. Vertebrates, including cows, hogs, dogs, salamanders, snakes and humans, use a circulatory system to do the job. Air is taken into the lungs where the oxygen is transferred to the blood. The blood is pumped around to cells in the animal by the heart. The system works pretty well.

But it is not the only system used by animals to supply oxygen to cells. In fact, the majority of animals don't have lungs and can't use such a system. These animals are the invertebrates. Invertebrates don't have backbones. They also differ from the vertebrates in other important ways, including how they breathe.

Invertebrates, including the insects, get oxygen to their cells through a series of air-filled tubes called tracheae. These tracheae run within a few cell diameters of each cell in the insect body. At that point, the oxygen diffuses from the tracheae to the cell.

That brings us to another difference in the breathing system between humans and insects. We all recognize that our nose and mouth are the openings that allow air to get to our lungs. Insects, in general, use openings called spiracles to do that job. There are a few exceptions, though. Some very small insects can get the oxygen that they need by diffusion through the cuticle; however, most have spiracles.

Spiracles are openings on the sides of insects that resemble portholes on the side of a ship. These openings are located on the thorax and abdomen of the insect. The number of spiracles varies between insects. The maximum number is 10 pairs; such a system is called holopneustic (meaning complete breathing) by scientists.

Not all insects have a full complement of spiracles. Some insects, like fly maggots, have only one or two pairs of spiracles functional. These insects are specialized for living in liquids, such as water or fluids of rotting material.  

Humans use active ventilation to get air into an out of their lungs. We contract and expand our chest cavity by contracting or relaxing the muscles of our diaphragm. This forces the air out of our lungs or allows air pressure to fill them up.

Insects generally do not utilize active ventilation. They just let the air move in and out of the spiracles passively. They do have muscles that can be used to close the spiracles when necessary to reduce airflow. When insects need additional oxygen in their system, they increase airflow by telescoping the abdomen. This is much like physically forcing air into and out of human lungs by chest compression during CPR.

Because insects don't need to force air into lungs like mammals, they don't have noses. They do have a proboscis, however. Some human noses of rather large size have sometimes been humorously called proboscises. Insects do have proboscises, but they aren't used for breathing. An insect proboscis is just used for eating!

 

 

Writer: Tom Turpin
Editor: Olivia Maddox