There are a LOT of myths and speculations about this phrase but the most probable is believe to be from 17 and 18th Century England. Jonathan Swift in “A Description of a City Shower” describes the dead cats and dogs that float along the streets during a heavy storm.
This saying is from ancient Rome and actually has to do with the Dog Star, Sirius. It is so named, because it is the brightest star in the Roman dog constellation, Canis Major. The “dog days” are often though of as the “hottest days of the year,”
Anyone who has raised a puppy can understand the meaning of this one: do not stir (wake up) anything that may cause trouble or an argument. The wiseGEEK says it refers to the way most dogs react if they are suddenly awakened—by biting or lashing out. However, we all know that even if your dog does not lash out immediately, if you wake it up, it can get into trouble so it’s better to let it sleep.
It is quite amazing how many sayings we have that involve dogs, but where did they come from? It makes sense that we would reference them in our vernacular considering how close we are to them, but surprisingly, they are not always referenced in a good light.
However, day labor “grunt” workers have also been referred to as dogs (derogatory). In this case, working like a dog may be a bad thing; not that you are working really hard, but that you are working hard and low on the totem pull, i.e. not worth much.
— My father works like a dog everyday. We make him take a break on holidays.
— My mom worked like a dog her whole life doing domestic work and saving every penny so we could go to college and have a better life.
— I didnt study at all during the semester so now Im working like a dog to try to finish all the material and pass my exams.
— One of the biggest myths is that we have to work like a dog to make good money. Those who work the hardest are usually the poorest.
— We were working like a dog all day pulling weeds in our garden so Im exhausted.