What is the origin of the idiom "have ants in one's pants" and when to use it?

The idiom "have ants in one's pants" originated in the United States, particularly in the early to mid-20th century. It is believed to have emerged as a colloquial expression within American English. The imagery of ants crawling inside one's pants was used figuratively to depict a state of restlessness, agitation, or impatience. The phrase is commonly used when someone is eagerly awaiting a particular event or outcome, such as before a performance, a job interview, or the start of a vacation. It can also be used to describe a person's general energetic or hyperactive behavior, especially when they are unable to sit or stand still for an extended period.