If your tarantula is already an adult, it is important for you to make an underground shelter for it, since most adult American tarantulas will not dig a burrow. On the other hand, most Asian tarantulas will do it constantly. For your tarantula to feel comfortable, it should feel protected by walls. This is where your imagination can start to work.
If your tarantula is a ground-dweller, you can use many items that will work as shelter, even soda containers!
Once your tarantula is well located in your terrarium, you must understand that its burrow begins from the cover down, and therefore, you should never bother her, and please, never change the objects inside the terrarium, especially its substrate! These are her home and her knick-knacks! If you change them, it will mean to her that she has lost her home. Instead, only pick up her waste, but leave all the webs. She knows best what she needs them for.
If your tarantula is only a baby, which is the ideal case, try to put pieces of bark on the substrate. This will serve as a roof while she builds her home for the first time. This is fascinating, just give her a roof, and she will start to dig.
Here, are shown pictures and a video with ready-to-use shelters made of refuse, or items that you can easily find in a hardware or plastics store.
As you can see, the purpose is very clear, to provide a place where she can hide and feel safe at home. Although, I will tell you something, it´s only a theory, but I believe that a tarantula that already feels safe rarely uses her cave. I think that she considers the entire container to be her cave! And this is why I should say again that you should not bother your tarantula, except for bare necessities only, meaning cleaning, water, and food.
If your tarantula is a tree-dweller, don’t worry, even if it sounds complicated, it’s not!
By placing your fish tank or container vertically, you will achieve more room for her. She usually moves vertically. Once you place a substrate of at least 15 cm deep, place some wide branches. She will make her burrow between the glass and the branches. If you can, place a big piece of bark against the glass, making a half-pipe against the wall, with an entrance on the top. Poecilotherias like this a lot. You can also try this with your Avicularia or other arboreal spiders. Don’t place a lot of decorative items, since these make hunting more difficult.
Place a big recipient with water, either in the middle section of your container glued on with silicone, or on the bottom of the tank. I know that many places recommend that you spray the containers for humidity, don’t do this! It is very annoying to them. Just keep the substrate a little damp, and that will be enough.