The thermometer is in the tank, there is a probe that reads the "outside temperature" which is stuck to the back side in the middle of the tank (just above the eco earth). The actual thermometer itself measures the "indoor temperature" (which is always alittle high because the light is so close to it.) and it also measures the indoor humidity, so the actual thermometer has to be in the tank (but it's water proof)

He's probably about maybe 2 inches long, but he did eat for me until the other day.