@Monotonous
Well, it's only because they're really small. Scientifically, the reason bugs can carry such "large" objects is because of their small size; their muscle to fat ratio is almost nonexistent. They basically don't lift much besides the object. Since we are much bigger and heavier (containing much more fat than muscle), we have to lift not only the object, but also the weight of our much larger bodies.
A bug that big would probably be a much stronger than a human, but nothing nearly as big or heavy as even 5x his size.