>>Are they arboreal, terrestrial, or fossorial?
I suspect they are terrestrial and partially fossorial in the wild.
>>keep at room temp, and 50-60%RH.
I keep mine in my snake room (which varies from 70°-78°F) without any other form of heat and they do just fine.
>>Anybody using naturalistic viv for habitat?
I keep mine is aspen as well. I think they would be pretty hard on a "naturalistic" setup because when mine eat, they tend to drag the rat around the cage and twitch and thrash (even though I feed F/T). They would trash a naturalistic setup during this process.
You could remove them for feeding, but anyone who puts his hands into a Black Milk's cage when there is rat smell in the room is taking his life into his hands, IME!
>>Anybody try the coconut eco-earth stuff?
I bought a bunch of that stuff a few years ago in bulk from LLL. I used it for all my snakes and after a few weeks I sold all the unopened packs at an expo. That stuff is VERY dessicating and I found that most of my snakes (including dry tolerant species like Trans-pecos Rats, Sandboas, Western Hogs, alterna) had shedding trouble and generally didn't fare well on it unless I sprayed it down (i.e. SOAKED it) every few days.
I finally longed for good old aspen, and went back.
It did look good, it just was too much work to prevent dessication. If you want something dark that holds moisture a little better, try cypress mulch if it is available in your area. It is cheap and as long as you remove the big chunks and keep it moist, it is a great "naturalistic" substrate.
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Chris Harrison