Spider size
is limited by their respiratory system. Spiders have 'book lungs' (and insects have tracheae) that are not capable of delivering oxygen to interior tissues if the body size becomes too large. So the biggest spiders and insects we see today are about as large as such creatures can get (which is quite large enough, thanks). Sea-dwelling arthropods, such as crabs and lobsters, are less constrained and hundreds of millions of years ago could grow to a couple of metres in length.
Biting the hand that feeds IT
