por si las moscas*
* for if the flies
It means that you're doing something not because it's necessary, but "just in case".
Note: The origin of the expression goes back to when there were no refrigerators to store food, so that meat needed to be covered or else it would've spoiled and flies would've come.
"Me he comprado un boli más, por si las moscas."
"I bought an extra pen, for if the flies."
Submitted August 2020
Confirmed by 10 people
<h2>por si las moscas</h2>
<h3>Literal translation: por si las moscas</h3>
<p>It means that you're doing something not because it's necessary, but "just in case".</p>