These giant bugs have a problem, and I can think of only one way out for them. Their joints must be made of some very hard material (to minimize wear) with excellent mechanical properties (to withstand the immense stresses involved), and only one material will fit the bill - diamond. You scoff? Diamond is only carbon, and living things have a lot of experience in manipulating carbon. So why didn't the characters in Them! notice that the giant insects had diamond-lined joints? In Them!, you'll remember, the giant ants are finally defeated by burning out their nest with flamethrowers. As I said, diamond is just a form of carbon, and like the more prosaic forms will burn quite nicely. The evidence literally went up in smoke.
This article also includes giant squids, attacking the Golden Gate bridge, and suffering massive subdural hematomas as a result.