What kind of frog do you have? Are there other live plants in the vivarium other than the palm? Darts do well with live plants such as vining plants, bromeliads, ferns, etc. Almost all darts climb glass, at least as youngsters. Some of the small thumbnails seem to use it as a recreation area and will even lay eggs on the glass. Some of the heavier ones may quit doing this as they get older. The only frogs I've never seen climb glass have been the Phyllobates terribilis. Fruit flies tend to climb upward, and a small dart can climb up and get them off the glass, but it's easier if you have lots of plants and a background or corkbark, etc. Try to sprinkle them on the plant life rather than next to the glass. You should also be dusting your fruit flies with vitamin/calcium powders, which will temporarily inhibit their climbing ability.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus