They may make your skin crawl and you might wish to think of them as a lower life form, but insects have a remarkably elegant and simple way of delivering oxygen to their body and removing the carbon dioxide waste.

Insects have a tracheal system rather than the complex respiratory (lungs and stuff) and circulatory (heart and blood vessels etcetera) systems we use to breathe and transport gases.  As vertebrates, we have to move the respiratory gases (oxygen and carbon dioxide) through two convective (physical moving of the gases through fluids) and two diffusive (passive movement from high to low concentration) processes (stay tuned for details in a future blog!).  The two convective processes (in the lungs and the circulatory system) cost energy.  In comparison, many insects move the gases through the tracheal system via simple diffusion which is a passive process that doesn’t require any energy.

Insects have tiny holes in their abdomen called spiracles (usually one pair per segment – see diagram).  Each spiracle is an opening to a tube or trachea and this tracheae system spreads throughout the body of the insect to allow oxygen from the environment to travel directly to each cell (and the carbon dioxide waste to return to the environment).

In small insects, the distance between the outside environment and the cells which need the oxygen are short enough for the oxygen to travel by diffusion (passive movement) alone.  The longer distances in larger insects need an additional way of moving the gases.  The larger insects pump their abdomens (by squeezing their muscles) moving the gases in their tracheae and helping to bring fresh air into the system.  The gas moves via convection when the animal pumps its abdomen and although it is a helpful way of moving gases when the distances are too long for passive diffusion alone, it costs energy and it too has its limitations.

The design of the insect respiratory (breathing) system is thought to have limited the maximal size that insects can grow to.  Even with abdominal pumping, there is a limit to how long the tracheae system can effectively transport the respiratory gases (oxygen and carbon dioxide).  The largest confirmed weight of any insect is of the giant Weta (Deinacrida heteracantha) at 71g.  Although this is larger than an adult mouse (~20g), many vertebrates with their more complex respiratory system are considerably bigger, the largest, the blue whale, weighing up to 180 tonnes.  So perhaps our very convoluted, complex and energetically costly vertebrate respiratory system has some advantages after all hey?  I hope you’ll join me to explore it in a future blog someday soon….