keeping crabs with other creatures in terr.

Question
I guess I should have been more specific. The terrarium is 8ft by 6ft by 4ft tall. The upper portion stays at about 85-90 deg F with 80-100% humidity and the lower part stays at about 70 deg F with many basking spots that reach 90-100 deg F. It stays at the lower end by the aquarium part and warmer on the other side. The humidity is around 50% on one end and and goes up to 85-100% on the other end depending on where you check it. There are many little hills and valleys with rock formations that create many hiding spots. It is also very heavily planted except in one small valley that is more bog like with nothing growing. I use a fogger in the morning and in the evening so the humidity fluctuates daily as it does in nature. I worked on specifically making microclimates for 5 years before ever putting a live creature, other than plants, in the terrarium. Because of the differences in temp and humidity the inhabitants stay in their own areas for the most part. I have a large section approx. 1.5ftx1.5ft on the bottom that nothing lives in. There is never any critter hanging out there or even just visiting. it has a shallow pool maybe 1/2 inch deep(shallower sometimes depending on when I water) and very little plant life. Just some rocks and coconut fiber. The humidity there is usually over 75% but never below 70%. I have worked so hard on making this whole thing inhabitable by many species and I don't like not having anything in this large section so I wanted to put small hermit crabs in there. My 12 y.o. son has a 55 gal tank in his room set up for hermit crabs so he would take them when they got too large for my enclosure. Hope this puts your mind at ease. I did not just throw this thing together. I built it from the ground up, including the actual enclosure itself, paying very close attention to detail. This has been my pride and joy for about 8 years now and everything has lived peacefully together for 2 years.
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-----Question-----
I have had a terrarium with 4 red eye tree frogs, 1 green anole, 3 house geckos, and about a 5 gallon section made into an aquarium with various fish for 2 years or so now with no problems. My question is this. Can I add hermit crabs to the terrarium? The daytime ambient temp is 76-78 F and nighttime is 68-70 F, humidity 75-80% usually closer to 80. If it's is not a good idea I would like to know why, not just "don't mix species it doesn't work" because I have successfully mixed these species for more than two yrs now. Thanks in advance!
-----Answer-----
Dear Josh,
thank you for your question.
Unless the terrarium is way bigger than average (I'm talking more than 2 yards edge length here), mixing species from different habitats is not a good idea, at best it's a compromise, at the expense of the well-being of at least one of the species.
The reason for this is that it's very hard to create microclimates in small enclosures and that the animals have no way to really hide from each other, making it very stressful for them to be kept with another species. The humidity is too high for both the house geckos and the green anole, the prefer a humidity of only 60-70% and it's too low for the red eyed-tree frogs, who need a humidity of at least 80%, better more. It's not enough for them to die of, but they would definitely feel a lot more comfortable in an enclosure of their own that has perfect conditions for each species.

Frogs can carry disease that may infect the crabs and the hosue geckos may try to prey on the crabs. The frog secrete a liquid from their skin that may harm the crabs, especially when the crabs try to climb over them (which will stress the frogs a lot, too). Crabs need a lot of room for themselves, at least a 10g for about five small crabs and they will outgrow the 10g in no time. So I highly recommend keeping them in an enclosure of their own.
I hope I was of some help to you
Jennifer

Answer
This sounds awesome, do you have any pictures online of the terrarium? I am sorry for lecturing you, but you won't believe how many people just throw anything that takes their fancy together in a 20g...
I'm still a bit worried about the frogs, though, because there is at least one case of a crabber loosing all crabs because newly bought crabs from a pet shop brought in some disease they probably got from the White's Tree Frogs they were kept with. They are also excellent climbers and won't stay at the bottom of the tank (the basking spots will probably be a favourite spot), which may cause stress for the herps. But they will love all that floor space. You will need to add a salt water pool, many crabs love to bathe in it and they need it to survive (except Coenobita clypeatus/Purple Pinchers, but they like to drink it anyway and it helps them to molt better).
Jennifer