You can make the characters travels in fear from the beginning, fearing an ogre would come out, then the big bug appear, the character sigh in relief thinking it is just a big bug and have confident to fight it. Then further in the travel, when they have more confidence, they heard sounds, thinking it was a big bug, but then petrified in fear because it is an ogre.
The story should have some-kind of folklore saying if you smell an ogre, run and never stop. Something like that.