Aliens Stole My Underpants

To understand the ways
of alien beings is hard,
And I've never worked it out
Why they landed in my backyard.

And I've always wondered why
on their journey from the stars,
these aliens stole my underpants
and took them back to Mars.

They came on a Monday night
when the weekend wash had been done,
pegged out on the line
to be dried in the morning sun.

Mrs Driver from next door
was a witness at the scene
when aliens snatched my underpants -
I'm glad that they were clean!

It seems they were quite choosey
as nothing else was taken.
Do aliens wear underpants
or were they just mistaken?