Kristina said:I use wine rather than sugar water - Take a glass, fill it half full with wine (or some fruit juice with a little vodka, whatever you may have on hand) and cover it with plastic wrap. Poke a few small holes in the plastic wrap, and the flies will go in to drink, get drunk and drown
I don't feel that one substrate is worse than the other when it comes to the flies. It isn't the substrate they are after, it is your tortoise's food. Picking up the food as soon as your tort is done eating will help nip them in the bud as well.
Kristina said:Neeeeeeerrrrruuuuummmmmm SPLASH! Bzzz....Bzzzz....giggle....gurgle....hiccup....squeak! Silence.....
Does that help the imagination at all?