Size Differences

The difference in sizes of insects and vertebrates accounts for their very different circulations. Insects range from about a thousandth to a tenth of a meter long, while terrestrial vertebrates range from about mouse size up to five meters. There is very little size overlap between these two groups. Thus, very few insects are as large as the smallest birds or mammals.

A large difference in the number of species — estimated to be of the order of more than a million for insects and twenty thousand for terrestrial vertebrates associates with this size difference. Additionally, insects have short life cycles, and there are many more of them. Insects are very successful at remaining small in air on land and avoiding water loss, as the surface to volume ratio of insects is very high. Vertebrates, on the other hand, have a much lower surface to volume ratio, and they successfully support large bodies in air on their internal mineralized skeletons.

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