Why were prehistoric insects so big

  • 1 The atmosphere was more suitable

    During prehistoric times, the atmosphere was more suitable for growth. The air was warmer, moister and contained more oxygen. Earth's atmosphere used to contain 31-35% of oxygen compared to the 21% we have now.

  • 2 Insects depend heavily on oxygen

    Insects don't have lungs but they absorb oxygen through pores in their bodies. Thus, an increase in the amount of oxygen can directly contribute to the growth of some insects. See why do people find insects disgusting.

  • 3 They were less likely to be eaten

    According to one theory, the large size of some insects made them less likely to be eaten by other creatures and this is why the large species survived for some time.

  • 4 They had to grow to absorb less oxygen

    According to another theory, insects had to grow big to avoid oxygen poisoning which might result from absorbing too much oxygen. According to this theory, insects grew so that they absorb less oxygen compared to their body size.

  • 5 Reduced oxygen reduced their performance

    As oxygen started getting lower, the performance of large insects was reduced and so they were easily eaten by other birds. This is one explanation why insects are now smaller.

  • 6 Reduced oxygen killed the big insects

    As oxygen levels decreased, the reduced oxygen affected the large insects which needed more oxygen to survive. As time passed, the large insects didn't manage to survive.

  • 7 They were later eaten by birds

    According to one theory, the rise of large birds was one of the reasons giant insects disappeared since the large ones were easily spotted by giant birds.