Blowflies are large (1/2 inch long), metallic-colored, and have a bristly appearance. They often fly in swarms and are most easily identified by their size and their bristly appearance.
The best way to get rid of blowflies is to eliminate their food sources by thoroughly cleaning your kitchen and bathroom. You can also use commercial fly traps or bait. If you have a severe infestation, you may need to call a professional exterminator.