Porcellio or Armadillidium sp. (?) (Woodlouse).
 
 
 
Size: approx. 6-8 mm. Photo: 08/27/11, 11 am.


Woodlice are crustacean with a rigid, segmented exoskeleton and fourteen jointed limbs. They need moisture because they rapidly lose water. 
 

 
bug guide (the small photo):
http://bugguide.net/node/view/569018
wikipedia:
http://en.wikipedia.org/wiki/Woodlouse