What are mothballs used for?

"I’ve heard that they can work to keep some pests away, but what are mothballs actually used for?"

Mothballs are small pellets of chemical pesticide. Their original (and only legally approved) purpose is to protect natural fiber clothing and textiles from clothes moths and other fabric pests.

They work through a process called sublimation: the solid slowly turns into a gas, releasing toxic fumes that can kill moth larvae in an enclosed space. To be effective, they need to be used in an airtight container (like a sealed garment bag or storage bin) where the fumes can build up to a concentration high enough to kill pests. Left out in the open, they're largely ineffective.

Because mothballs are classified as pesticides, they're regulated by the U.S. Environmental Protection Agency (EPA). Using them in any way not specified on the product label, including placing them outdoors or in open spaces, is illegal.