How Big is a Big Insect?

io9.com has an article on the Giant Weta Bug, reported to be the world's largest insect.  Now it may be that all campaign settings have examples of giant insects like swarms of giant bees and colonies of very large ants, but how big do you make the normal instects in a campaign setting and still retain some credibility?  Well, the Giant Weta Bug has just raised the bar for all of us!