This is because the water turtle needs to overwinter, and it dives through the crack of the door to find a place suitable for overwintering. Another important reason is that there are a large number of insect sources near your home, and the environment (dark and humid, with high humus content in the soil) is suitable for their growth.
To put it simply, I eat everything, and my diet is very miscellaneous.
For information about terrapin, you can have a look if you are interested:/view/704049.htm.