If you are looking for the strongest adhesive in the world, you are going to need a microscope. Apparently, Caulobacter crescentus, a form of bacteria now holds the record for strongest adhesive; natural or synthetic.
How strong is it?
From LiveScience.com. "The adhesive can withstand an enormous amount of stress, equal to the force felt by a quarter with more than three cars piled on top of it. That's two to three times more force than the best retail glues can handle."
Now if they can just figure out how to get the stuff out of the test tubes.