To find the length of BD, we can use the distance formula.
The coordinates of B are (-3, 6) and the coordinates of D are (-3, 1).
Using the distance formula:
BD = √((-3 - (-3))^2 + (1 - 6)^2)
BD = √(0^2 + (-5)^2)
BD = √(0 + 25)
BD = √25
BD = 5
Therefore, the length of BD is 5 units.