Flys or Flies – What’s The Difference

Using Flys or Flies incorrectly is a common grammatical mistake that is made even by native English speakers.

Flies – Is the plural of a fly the insect or something that flies through the air (planes, birds, Superman, frisbees, etc.). It’s also used colloquially to mean something that moves quickly.

Flys – Is normally wrong except in a few obscure instances, which I’ll explain below.

Where I see the mistake most often is when people are referring to the insect:

‘There was a fly on the fruit, which quickly attracted other flys – This is wrong because the plural of a fly, when referring to the insect, is flies.

The sentence should be:

‘There was a fly on the fruit, which quickly attracted other flies

Flys or Flies

When trying to figure out whether you should use flys or flies, let’s understand the similarities and differences between the two words.

Flys and flies are homophones, meaning that they sound the same but have different meanings. They can both be plural nouns, meaning that they are used to indicate multiples, but they do not refer to the same things.

When to use Flys

Flys can be the plural of the word fly, but it only applies in a few specific instances:

  • The first talks about fabric/zipper on the crotch area of pants (trousers in British English), something that has been referred to as a “fly”. You have probably heard of this term colloquially, but it comes from the term in England that once referred to the flap on a tent, and the term was adapted to clothing
  • Another instance where you would use flys would be referring to multiple fly balls in baseball. These are balls that are batted high into the air, and while they occur frequently you are more likely to hear “fly balls” than you are “flys”
  • Flys can refer to multiples of these carriages from the 1800s. Because they were small and lightweight they were easier to transport quickly, seemingly “flying” compared to other bulkier carriages
  • The last definition of “fly” that can be pluralized this way refers to the area over a theater stage. This is more commonly referred to as fly riggings, but flys could be appropriate in this context. You probably will not need to know this unless you work in a theater.

When to use Flies

You are more likely to see flies:

  • The first is the pluralization of the insect fly, such as a housefly or a butterfly. When you refer to multiple of these bugs the word changes into flies, so you get house flies or butterflies
  • The second is the third person conjugation of the verb fly. Anytime someone is referring to another person present or in the future flying in the third person (using a name or pronouns like “he” or “she”) they would use flies.


That might make sense to you, but seeing these words in action should help. Check out the examples below for a more in-depth view of the difference between flys and flies.

Examples of Flys

There are four different subjects where using flys would be correct:

  • They covered the flys of their jeans
  • The baseball game had more flys than most games
  • The flys were efficient carriages when it came to timely deliveries
  • Rebecca’s favorite places to check out in theaters were the flys.

As long as you are speaking about a flap of clothing, fly balls, fly carriages, or fly riggings in a theater then using flys is correct.

Examples of Flies

Using flies is easier to remember because you will use it more often.

  • Mary was horrified when a swarm of flies landed on her food
  • Astrid flies past me, obviously in a hurry to her next class.

Using flies simply shows up more because its roots are more common.

Some Common Phrases that Use Flies

  • Flys or Flies a Plane – It’s always flies a plane
  • He Flys or Flies – It’s always he flies, she flies
  • Time Flys or Flies – It’s always time flies
  • Flys by or Flies by – Yep, you’ve guessed it, always flies by

How to Remember Flys vs. Flies

There is no hard and steady rule for remembering the difference between flys and flies, but you can get the idea in your head that you will use flies more often.

Flies is affected by the same rule as a lot of other words, such as:

  • Baby/babies
  • Pantry/pantries
  • Candy/candies

Learning that ‘y’ is often replaced with ‘-ies’ is an easy rule to commit to memory.

Test Yourself on Flys vs. Flies with These Sentences!

  • With this many ____ in a baseball game, the outfielders are hard at work
  • Sam ____ in on Sunday morning
  • The ____ seem to be attracted to the horses
  • It was no wonder the grocer preferred ____ to other, slower carriages.
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About Jon Wright

Jon has worked in Digital Marketing for over 20 years, mainly for large enterprises. He now runs an eCommerce Agency that helps merchants build and grow their stores. He writes about SEO, CRO amongst other things.

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