http://www.wikipedia.org/
This can be quite a tricky business. Differant species of tarantula require differant humidity levels. It is usually between 65-70 or for species in tropical areas 70-90. Please look up/research information about the breed of tarantula you are going to buy and see their correct humidity levels. Wikipedia is usually quite good for this.(see the address above). Just type in the species of tarantula into the search bar and valla.
To put the level of humidity up simply spray to substrate at the bottom of the vivarium, simple. Please be careful not to spray your tarantula at the same time as he/she won't be to happy about it.
