Really Big Bugs

« Getting “Campy” | Home | Evolutionary Tail Fins? »

By Linda | March 31, 2008

There was a time in Earth’s prehistoric past when insects grew to enormous sizes. Fossil records reveal that there were once dragonflies with the wingspan of a hawk and millipedes that were perhaps 6 feet long.

Scientists have long theorized why modern insects should have elvolved to such dramatically smaller sizes. The answer appears to be linked to the nature of an insect’s respiratory system and to the composition of Earth’s atmosphere during the height of “insect gigantism”.

Insects breathe through a network of air filled tubes that deliver oxygen directly to their cells. These tracheal tubes, especially in the leg, take up more room in larger insect specimens.

The oxygen content of our present day atmosphere is about 20 percent. More than 300 million years ago, there was 31 to 35 percent oxygen in the air. That means that the respiratory systems of the insects could be smaller and still deliver enough oxygen to meet their demands, allowing the creatures to grow much larger.