Why are insects so small? The main reason that insects, for example the Weta, are so small when you compare them to their prehistoric ancestors, is because of the oxygen in the air. All insects are common in that they have particularly unique methods of gas exchange. An insect has little holes, called spiracles, which are the site of entry and exit of oxygen and carbon dioxide for the insect. These are located in the thorax and the abdomen, these lead into trachea which are chitin lined tubes that remain entirely separate from the blood stream. These then lead into tracheoles which line cells and allow for oxygen to diffusion in and out of cells.
This method of gas exchange is extremely limited. This is because the insect’s method of gas exchange cannot be ‘accelerated’. A mammal’s gas exchange can be regulated by lungs which can be accelerated as too speed up gas exchange. This cannot happen in an insect, it is also inefficient as the larger the insect is the more oxygen it needs however it can’t use active transport to move oxygen into the trachea. This oxygen is diffused which is a slow process so therefore insects in the current climate just cannot grow to large sizes.
However insects from 360 million years ago were a very large size, with Palaeozoic Era Dragonflies reaching up to 65 centimetres. This is because the oxygen level was so much greater. As the insect size is limited by oxygen levels, if the oxygen concentration in the atmosphere is greater than the insects size would get larger as its robust gas exchange system can support a larger organism with more cells.
This method of gas exchange is extremely limited. This is because the insect’s method of gas exchange cannot be ‘accelerated’. A mammal’s gas exchange can be regulated by lungs which can be accelerated as too speed up gas exchange. This cannot happen in an insect, it is also inefficient as the larger the insect is the more oxygen it needs however it can’t use active transport to move oxygen into the trachea. This oxygen is diffused which is a slow process so therefore insects in the current climate just cannot grow to large sizes.
However insects from 360 million years ago were a very large size, with Palaeozoic Era Dragonflies reaching up to 65 centimetres. This is because the oxygen level was so much greater. As the insect size is limited by oxygen levels, if the oxygen concentration in the atmosphere is greater than the insects size would get larger as its robust gas exchange system can support a larger organism with more cells.
I was reading an article that was shown to me by my teacher. This article outlines research in which scientists emulate prehistoric levels of oxygen. This was done by raising insects in identical habitats differing only in oxygen concentration. They found that dragonflies grew bigger and faster, this provides proof that insect size is wholly dependent on oxygen concentration. This experiment was conducted from birth, when dragonflies are just nymphs, they were separated, with 75 in at each oxygen concentration, this meant they could prove that the oxygen was a definitive cause of the size increase in prehistoric times.
This research can be used for when insects are crystallised in rocks such as amber, by comparing their tracheal size they can deduce how much oxygen there was in the atmosphere which means they can roughly pinpoint when the creature was alive. They can also find the oxygen concentration in the atmosphere from insects at known points in time to confirm original theories about oxygen levels. The researchers hope to study the dragonflies’ behaviour at different oxygen levels to further understand prehistoric giant insects and their place in the food chain.
I chose to write about this article as I find it very interesting when I was shown it but also that in our a-level syllabus for biology we learn about insect gas exchange which is featured heavily in this article
http://www.wired.com/2010/11/huge-dragonflies-oxygen/
This research can be used for when insects are crystallised in rocks such as amber, by comparing their tracheal size they can deduce how much oxygen there was in the atmosphere which means they can roughly pinpoint when the creature was alive. They can also find the oxygen concentration in the atmosphere from insects at known points in time to confirm original theories about oxygen levels. The researchers hope to study the dragonflies’ behaviour at different oxygen levels to further understand prehistoric giant insects and their place in the food chain.
I chose to write about this article as I find it very interesting when I was shown it but also that in our a-level syllabus for biology we learn about insect gas exchange which is featured heavily in this article
http://www.wired.com/2010/11/huge-dragonflies-oxygen/