When you have pierced earrings, and you have lost the back to them, there is something you can do to keep them on. The little erasers on mechanical pencils can serve as very handy and yet very secure backs for them.
Simply take the eraser out of the mechanical pencil and stick the post of the earring into it. This will only work for post-earrings. The wire earrings are too thin and therefore bend too easily to be able to use the eraser trick in them.
As you can see from the picture, you do not have to buy mechanical pencils just to get the erasers off of them. You can buy just the erasers. They will usually come in a cylinder like the one below. This particular cylinder has enough erasers to handle three pairs of earrings.