Por si las moscas
/por see lahs MOHS-kahs/
To do something 'just in case' or 'to be on the safe side'.
💡 Understanding the Idiom
🎨 Literal vs. Figurative
Literally, this means preparing 'for if the flies' show up.
In practice, it means taking a precaution 'just in case'.
📝 In Action
Llevaré un paraguas, por si las moscas.
B1I'll take an umbrella, just in case.
Aunque el pronóstico es bueno, coge una chaqueta, por si las moscas.
B1Even though the forecast is good, grab a jacket, just to be on the safe side.
Guarda mi número de teléfono en tu móvil, por si las moscas.
B2Save my phone number in your cell, just in case.
📜 Origin Story
This expression has a very practical and visual origin. It comes from the age-old habit of covering food to protect it from flies. Even if you didn't see any flies at the moment, you would cover the food anyway as a precaution, 'for if the flies' were to appear. This simple, sensible act of preventing a common nuisance evolved into a general expression for taking any precaution against a potential problem, no matter how small.
⭐ Usage Tips
Use it as a Standalone Phrase
You can use 'Por si las moscas' all by itself. If someone asks why you're bringing a jacket on a warm day, you can just shrug and say, 'Por si las moscas.' It perfectly communicates 'just in case' without needing any other words.
It's All About Precaution
This phrase is perfect for any situation where you're doing a little something extra to be prepared. Taking extra cash, packing a snack, saving a document twice—all are great moments to use 'por si las moscas'.
❌ Common Pitfalls
Don't Connect it to Actual Flies
Mistake: "Thinking the phrase can only be used when there's a risk of insects or something dirty."
Correction: The flies are completely metaphorical now. The expression has nothing to do with actual insects and is used for any kind of general precaution, from weather changes to running out of money.
🌎 Where It's Used
Spain
Extremely common. It's a cornerstone of everyday, informal Spanish and is used by everyone.
Latin America
Widely understood and used in most countries, especially in the Southern Cone (Argentina, Uruguay, Chile). However, the phrase 'por si acaso' is often a more common equivalent in many regions.
🔗 Related Idioms
✏️ Quick Practice
💡 Quick Quiz: Por si las moscas
Question 1 of 1
If you grab an extra bottle of water for a hike 'por si las moscas', what are you doing?
🏷️ Tags
Frequently Asked Questions
Is 'por si las moscas' the same as 'por si acaso'?
Yes, they mean the exact same thing: 'just in case'. 'Por si las moscas' is a bit more colloquial and colorful, while 'por si acaso' is a more standard and direct equivalent. You can use them interchangeably in most informal situations.