fly

fly1 often taken as the type of something unimportant and trivial.
fly in amber a curious relic of the past, preserved into the present; alluding to the fossilised bodies of insects often found trapped in amber. The image was given a different slant by Michael Crichton's thriller Jurassic Park (1990) and the Spielberg film based on it, in which the DNA essential to the recreation of dinosaurs was retrieved from the animal's blood supposedly fossilized with the insect that had fed from it.
fly in the ointment a minor irritation that spoils the success or enjoyment of something; originally with biblical allusion to Ecclesiastes 10:1, ‘Dead flies cause the ointment of the apothecary to send forth a stinking savour.’
fly on the wall an unnoticed observer of a particular situation. Very often as a modifier, as in fly-on-the-wall documentary, which refers to a film-making technique whereby events are merely observed and presented realistically with minimum interference rather than acted out under direction.
fly on the wheel a person who overestimates their own influence. With reference to Aesop's fable of a fly sitting on the axletree of a moving chariot and saying, ‘See what a dust I raise.’