You go out to your mailbox to collect your daily delivery only to find a dryer sheet in the back of the box.
Is this some sort of prank or warning? No!
Your mailperson has probably put the dryer sheet in your box to ward off wasps. Wasps hate the aroma on dryer sheets and won't build nests there, protecting your mailperson and you from a nasty surprise.
Dryer sheets also work to repel ants which are also very sensitive to the scents on dryer sheets. You can place the sheets near water pipes or other openings they may have found into your home, and they will not come back.
So if you find a dryer sheet in your mailbox, leave it there and replace it if you find it is losing its scent. Wasp stings are some of the most painful insect bites or stings. A little freshness can prevent them!