reply to post by Big Raging Loner
Well let me start off this reply by stating for the record that I'm the proud keeper of seventeen separate tarantulas of varying species. I love
spiders. The thought of one five feet across makes me grin ear to ear and start mentally designing some for of leash set up so I can take one for a
walk. It also makes my dear little Malice (a Salmon Pink Bird Eater AKA Lasiodora Parahybana) at her paltry eleven inches seem tiny. Poor girl.
That being said, it is sadly rather impossible. Given the set up of a tarantulas lungs, they are incapable of growing much bigger than they already
are. Back in the days before there were dinosaurs, there were in fact spiders the size of dogs. This was because the oxygen content of our atmosphere
was so much vastly higher at that point, thus allowing their somewhat "primitive" book lungs to breath much easier. More modern spiders (bear in
mind, tarantulas are MUCH older and considered more "primitive") have a more advanced system of breathing involving a wonderful trachea/book lung
combo.
The problems with breathing having been stated, we must also consider the lovely exoskeleton of everyone's favourite arthropods. The reason that
none of those Giant Bug Movies could ever happen is, at a certain size, an exoskeleton would collapse under its own weight. This was no doubt one of
the many things the precipitated the rise of giant bloody lizards, the fact that they kept all their bones inside their body. A bloody good thing they
were able to grow so big, otherwise the spider's would've eaten them all!
). 
