The Parasite Class
I have a finch feeder outside the window where my computer sits. Most of my customers are the Texas lesser goldfinches, which weigh about 10 grams, or roughly the weight of two nickels, which is how much money I have left to rub together after buying their food. They eat little nyjer seeds, which they shell and eat with phenomenal efficiency. They are my personal parasite class, and I feel guilty if I let their feeder sit empty. It's quite amazing how much these tiny creature eat, though.
I'm a member of the parasite class myself, since I don't work for pay, and live off my pension and savings. I tend to think of the rentier class as parasites too, so it annoys the heck out of me when one of their members, like Willard R., inveighs against the people who get Social Security and other government benefits.