gadfly (noun) – a fly that lives on animals, or: an irritating person who asks questions all the time or who criticizes constantly

Here are some examples of how you can use gadfly:

The horse was flying his tail, trying to beat off the gadflies that bit his skin.

The Prime Minister opened the newspaper and after reading a few minutes said: “When will that gadfly finally tire of making fun of me?”

I wanted to taste some of the mouth-watering cakes, but there was that gadfly voice again in my head that told me: “And what about your bikini diet?”

The movie star had finally found the perfect hiding place where he could be free from those gadflies, the paparazzi.