These may or may not be warts. Although they can form anywhere on the body and be of various colors, they usually don't form on the back and stomach, and usually have rough surfaces. If it is a typical wart, many do commonly go away on their own, but some require treatment. Because it's a viral infection, they may come back, because the virus stays in the body for life.
There are many types of benign skin growth that would match that description, and unless they are itching or bleeding, or otherwise bothering you, treatment isn't necesseary until you want it done for cosmetic reasons. These include (pulled from http://www.umm.edu/dermatology-info/other.htm):
You can read about other, less likely, types of growths here: http://www.umm.edu/dermatology-info/other.htm.
Aside from non viral skin growths, another possibility is molluscum contagiosum. This is a viral infection that occurs on the skin. They also sometimes disappear on their own. They consist of pink bumps, or papules on the skin, and generally do not cause any problems. You can read more about them here: http://www.skin-disorders-guide.com/molluscum-contagiosum.htm
Can you go into more detail about why you don't think any of the above growths don't fit the description?