“Good night. Sleep tight. Don’t let the bedbugs bite.”

For most adults, it’s a familiar little rhyme, a throwback to childhood. For those in major cities like New York ― where real bedbugs turn once-happy people into balls of despair and anxiety ― it can also conjure a visceral sense of terror. Say it to anyone who’s dealt with the nightmare of bedbugs and watch them visibly flinch.

But when did this little rhyme appear on the scene? And what did it initially refer to?

Fossils and early texts indicate that bedbugs existed as far back as ancient Egypt and Rome under various names. Colonization and industrialization fostered their spread in North America, until DDT and other pesticides wiped out most of them in the mid-20th century.

The cutesy bedbug rhyme predates the DDT era, but today, it again has a too-real connotation. Over the past two decades, bedbugs have made such an aggressive resurgence in the U.S. that CBS deemed 2010 the “Year of the Bed Bug.”