Temperature of body of spider and intensity of metabolism and other functions of its organism, inheres in direct dependency from the temperature surrounding ambiences. Optimum temperature for keeping tarantulas is varies within 24-26°С, but small shifts of temperature up or down do not cause tarantulas any harm.
In the case with separate species of group 2 (for instance, Grammostola rosea), capable to carry significant reduction of temperature till 16°С, but for Megaphobema mesomelas from mountain cloud tropical rainforest of Costa-Rica the temperature over 23-24°С can be fatal.
Fall of temperature below 21°С for species of group 3, particularly tarantulas inhabitting biotops of lawland tropical brazilian rainforests and group 4 (from arid African areas) is extremely undesirable.
Observations in captivity shows that during summer period, when surrounding temperature sharply increases (over 30°С), many tarantulas can be noted being immersed in water bowl. So, at choice of temperature for keeping tarantulas is necessary to take into account particularities of concrete species. But in the main its mass tarantulas do not require additional heating and for normal life and development wholly content with the average room temperature.
On the other hand, possibility of artificial regulation of temperature for keeping has its advantage since allows to regulate intensity of growing of spiders, that can be important in connection with tarantula breeding with limited amount of specimens of the species.