Here’s one way to prevent ants from ruining your picnic — surround the tablecloth with parallel strips of electrically conductive material and attach them to a DC battery. Now any bug that crosses the border will close the circuit and get “a sensation which will discourage further travel across the edge of the cloth.” (Humans will feel only “a slight tingling sensation.”)

This idea, patented by Richard Mahan in 1992, has a proud history — Thomas Edison tried essentially the same thing as a young man.