What's this strange behavior?

[Appreciate Creation]

Ok so you have a wild caught chalcodes. It's behavior might differ from one that was kept in captivity.

Wild caught tarantulas might be more defensive but not always.

Two reasons for more substrate. One you already mentioned, in case of a fall. The other one is deeper substrate holds more moisture at deeper levels. The less amount of sub means moisture will evaporate faster.

I've been to the Phoenix area many times since 1996 in all weather seasons. Even though it's a desert environment tarantulas burrow to seek moisture. If they didn't they would not survive long living a life predominantly on the surface. Not just from lack of moisture but also from predators.

The fact you found it by your pool should indicate it was searching for water, possibly.

Aphonopelma chalcodes is a very hardy tarantula and is very forgiving of husbandry mistakes. You do not want to drench it's enclosure so it's like a swamp.

What I do with mine is make a tunnel in the substrate in the corners going straight down with tongs. I use a bottle with a nozzle as it shoots a stream of water which is better for targeting. I shoot water in the corners until the lower layers of sub has a good amount of moisture. The top layer will always dry out faster. The object here is not to overdo it and if the tarantula is seeking out more moisture it will burrow down to it.

That makes sense! Thank you so much for the insight!

The Arizona blonde's that I've dealt with do the exact same thing.

Interesting! Would you be down to share what their tank setups were like. I'm curious if we can find a correlation between the tank setup and behavior, although Arachnophobephile provided some great ideas on things i can fix with mine.

 

[Ratmosphere]

I keep them on deepish coco fiber, no sand.

 

[Olan]

Based on my observations, I think they do this some times to “sun” their abdomen, to raise it’s temperature during digestion or if the environment has just warmed up after a cool period.

i think they do it more often in spring, after coming out of a semi-hibernation period.

 

[Gevo]

I'm not sure why yours is doing this, but I know that with Grammastola species, this is a common position, especially when they're feeling the need to look bigger (hence why it's thought of as a defensive position). My G. pulchra spent several weeks in this pose after his last molt, and I chalked it up to him needing to get resettled after molting, maybe using the pose as a sort of pre-emptive defense while he got his bearings and figured out what threats were or were not around after he'd been holed up for many months. The behaviour stopped after about a month. I figure if they can change dispositions and whatnot after a molt, it makes sense that they'd need a resettling period post-molt even if they're in the same enclosure. Did yours molt recently, perhaps?

Either way, it's not something to be overly worried about, though you can still take others' suggestions into account. I have a B. hamorii that also likes things quite arid, and I give her lots of room to dig (and she does! She's got a whole multi-chamber system now that's super cool, even though most stuff you'll see about them suggests they don't like to burrow much in captivity), and I keep her soil dry for the most part and just moisten the bottom layer once every few weeks or so, but I always make sure she has a full water dish.