First of all, welcome to the forum.
Poison darts got their name from 2 species of Phyllobates, P. aurotaneus and P. terribilis that were used by the natives to poison their blow gun darts (not arrows) to bring down prey. They wiped them against the frogs' skin, usually stressing the frog to do this. While all dart frogs have skin toxins, these are gradually lost in captivity and in captive bred frogs. There are various reasons for this, not always clear, but a change of habitat and diet is clearly indicated. Their jewel like coloration is a warning to predators: "Watch out! I'm poisonous." This also makes many of them very confident in captivity, so (with exceptions, of course) they are generally very bold frogs that come out to be seen.
We use a generalization of 5 gallons per frog for convenience, but it often depends upon the species of frog. 35 to 60 gallons would not be a waste of space, because even the terrestrial frogs use all levels of a tank. The thumbnails, which are supposedly more arboreal, will also hop around on the ground. I've repeated this so many times it is redundant, but when you think about it, a huge forest canopy and the ground area are not duplicated in a tank, however high it may be. In the forest, both arboreal and terrestrial frogs will utilize the entire height and more than we can provide in a vivarium at a any particular level. So either way, these captive frogs are using only a small fraction of the ups and downs they would ordinarily use in the wild. I have none that can't be found at one time or another at all levels of any of my tanks. The thumbnails will climb glass, and the younger of the heavier terrestrial frogs will also do this occasionally. The terrestrial leucomelas, galactonotus, P. terribilis, D. auratus, may sit in the upper regions behind or in bromeliads, as well as hunt and splash in the waterways at the ground level.
I have a personal opinion that bigger is better, even with the tiny thumbnails. A couple of 33 gallon hexagonals each contain only a pair of thumbnails--pumilio and imitator. Four tiny D. reticulatus are in a 30 gallon, and are all over the place, top to bottom, and even diving in the waterway under the rocks. Most are active, diurnal frogs, and with some exceptions, you will see them all over the place.
They are actually nothing like tree frogs.
I'm generalizing a lot, because different species and even individuals vary. The thumbnails (tiny arboreals frogs) are more athletic, but all are fun to watch.
One thing is for sure: You won't waste space by keeping them.
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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