Red worms (Eisenia Fetida) do best in temperatures between 55-77 degrees Fahrenheit, but can survive from 40-80 degrees F. Outside worm bins are subject to the elements and sometimes much more extreme temperatures in Summer and Winter. To remedy this a worm pit is an effective way to combat these extreme temperatures. The underground temperature holds a more constant temperature. Thermal inertia means that below ground temps. stay cooler that air temps. in Summer and warmer in the Winter.
I have built worm pits outdoors in South and East Texas, and they have done very well. A worm pit can be a simple worm bed that is dug several inches underground in a shady spot with a protective cover, or by placing a plastic pot or bucket halfway or more into the ground to keep out of the elements.
I keep several smaller bins indoors. Plastic containers make terrific worm bins, and can be kept odor free, and bug free indoors. You can purchase starter farms that are set up w/ bedding, food, castings, and hundreds of worms from TexasRedWorms.com.