Oxygen is one of the most important molecules needed for growth and to sustain life. Humans and other mammals take in oxygen through respiration. We breathe and inhale oxygen into our lungs, which then disperses oxygen to all tissues via blood blood flow. Other creatures in our world clearly do not have lungs, so they cannot use this method for dispersing oxygen through their bodies. In particular, the way insects breathe is interesting to study.
Insects breathe or gather oxygen through a branched network of tubes called tracheae. These tubes have openings, called spiracles, located on the thorax (chest) and abdomen. Oxygen passively enters spiracles, flows down the tubes, and ends up in liquid located at the bottom of each tube that helps the oxygen dissolve. This liquid then moves into other cells, to provide oxygen to other cells in the insect body.
You can see, under microscope, insects breathe or take in air through their mouths, but they seldom yawn. And this air through the mouth doesn’t provide needed oxygen to the cells because insects lack lungs. Instead of using air in the mouth to supply lungs with oxygen, it can be said that insects breathe passively. They must rely on oxygen around them entering their spiracles, making way down their tracheae to provide needed oxygenation of all their cells.
What makes the subject of how insects breathe fascinating is that theoretically, insects in a highly rich oxygen environment could technically become much bigger than today’s modern versions. For example, many paleontologists suggest that a lot of our modern bugs are tiny versions compared to giant insects that may have roamed the earth in prehistoric times. Due to the passive way insects breathe, life can’t be supported when insects are very large, since there would be no way to properly oxygenate all cells. Scientists believe earth used to have much higher oxygen content, however, meaning there was a proliferation of oxygen for insects to take in. This alone could explain why creepy crawlies of the past were very large — they had more available air to “breathe.”
As oxygen levels declined on earth, being of smaller size would have been of advantage to the insect. Since insects couldn’t breathe as much, survival may have been predicated on being more compact to provide healthy oxygenation to all tissues. Though it should be stated that there are still some pretty large insects in the world. They are mostly not, however, as large as those discovered in fossil records.
For instance, the largest dragonfly fossil found was thought to have lived 250 million years ago during the Paleozoic Era. Its wingspan was 30 inches (76.2 cm), and its body length 18 inches (45.72 cm). Clearly the oxygen rich environment and the way insects breathe benefited the early dragonfly, which had a wingspan about as wide as a toddler is tall.