Besides bills, you never know what you will find in your mailbox.

If you find a dryer sheet inside your mailbox, it’s not a prank, according to multiple news outlets.

There is an explanation about how it got there.

“I can't tell you how many times, especially during this part of the year, where I've opened up a box to see a little nest with 3 to 5 yellowjackets just chillin."

- U.S. Postal Service worker

Some United States Postal Service workers are using dryer sheets to keep from getting stung by wasps while placing mail in mailboxes.

“I can’t tell you how many times, especially during this part of the year, where I’ve opened up a box to see a little nest with 3 to 5 yellowjackets just chillin,” a letter carrier, under the username istrx13, recently wrote in a Reddit thread. “If I’m really unlucky, they will have made their nest at the very back of the box so I wind up sticking my hand in not knowing they are there. We all know how temperamental these little insects are … Last year alone, I was stung 10 times on 10 separate occasions.”

The user said the dryer sheet should be used only as a preventative measure. If the insects set up shop, the nest needs to be removed immediately by an expert.

“So please, if you one day randomly see a dryer sheet at the back of your mailbox, just know that your carrier more than likely put it there to deter these Satanic creatures from building their home in it,” the user wrote.