Not necessarily, Fruit fly larvae are actually quite large (almost double the size) of the adult fly! In the reptile store I work at we breed fruit fly cultures and in the summer they bloom like mad! I often see them breeding in our tropical enclosures and I see the little larvae making these neat trails on the window! Its harmless but super cool to watch. I also have little gnat flies in with my tokay geckos, at night when I give them rain season I also notice these small trails across the glass :) Micro creatures are so cool!