Fruit flies will show up where there's just about any moisture/food source commonly left out.. Contrary to popular opinion "fruit flies" don't only live on fruits.. All flies of the Drosopholia Melanogaster "complex" live on decomposing organic matter... and as well all know.. decomposition releases sugars bound up in cells..and that attracts the fruit flies.
-----
Lucien
1.0 Columbian Redtail Boa (BCI)
3.1 Leopard geckos (2 Blizzard and 2 het Blizzard)
0.1 Savannah Monitor
13 rats
12 Gerbils
2 Dogs
3 cats
1 Albino Corey (fish)