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When grading student writing, I see “flys” as one of the most common spelling errors — typically in contexts where it shouldn’t appear. The rule is straightforward: the plural of “fly” (the insect or the verb) is always “flies,” not “flys.” The only exception is proper nouns, such as surnames (e.g., “Mr. Flys”), but this is a name choice, not a spelling rule. If you ever doubt which form to use, the answer is “flies” — with certainty.
You’ll explains why “flys” is incorrect for plurals, shows you when and why “flies” is correct, and provides sentence examples that clarify the distinction. You’ll gain confidence spelling it correctly every time.
Key Takeaways
- Flies is correct for plurals — multiple insects, multiple acts of flying, or fishing lures.
- Flys is wrong — except in proper nouns (team names, person names used as brand names).
- The Y-to-IES rule — most words ending in consonant + y become -ies (try → tries, baby → babies, fly → flies).
- Flies as a verb — “She flies to Paris every summer.” (3rd person singular present tense).
- Quick memory trick — “Flies” rhymes with “tries” and “cries” and “spies” — all words that follow the same Y rule.
The Rule: Flies Is Always Correct for Plurals
The word “fly” can be a noun (the insect) or a verb (to move through the air). In both cases, the plural form is flies — never “flys”.
Fly as a Noun (the Insect)
Singular: There was a fly in my soup.
Plural: There were flies buzzing around the picnic table.
Example 1: A single fly landed on the window.
Example 2: The kitchen was infested with flies after the garbage can tipped over.
Example 3: I watched a fly crawl across the plate.
Fly as a Verb (to Move Through the Air)
Present tense, 3rd person singular: The bird flies south in winter.
Plural/3rd person singular form in other tenses: They fly together (present). She flies every week (present). The geese fly in formation (present).
Example 1: “She flies to London three times a year.” (3rd person singular present tense)
Example 2: “The planes fly overhead every morning.” (plural subject, present tense)
Example 3: “A hawk flies above the valley searching for prey.” (singular subject, present tense)
Fly in Fishing
In fly fishing, a “fly” is an artificial lure tied to resemble an insect. The plural form is also flies.
Example: “I tied three flies for tomorrow’s fishing trip — a dry fly, a nymph, and a streamer.”
Why “Flies” Not “Flys”: The Y-to-IES Rule
English has a simple rule for pluralizing words that end in a consonant followed by “y”: change the “y” to “ies”. The word “fly” follows this rule perfectly.
The pattern:
| Singular (consonant + y) | Plural (change y to ies) | Sound pattern |
|---|---|---|
| fly | flies | consonant + y → -ies |
| try | tries | consonant + y → -ies |
| spy | spies | consonant + y → -ies |
| baby | babies | consonant + y → -ies |
| city | cities | consonant + y → -ies |
| library | libraries | consonant + y → -ies |
Exception — when y is preceded by a vowel: If a word ends in a vowel + y, simply add “s” (no change to y).
Examples: boy → boys, key → keys, day → days (not “daies”).
Since “fly” ends in a consonant (the “l”) followed by “y”, it follows the “change y to ies” rule: fly → flies.
When Might You See “Flys”?
In standard English, “flys” is never correct for plurals or verb conjugation. However, you might see “Flys” in proper nouns — that is, when it’s someone’s last name or a brand name that deliberately uses the non-standard spelling.
Example: “Mr. Flys” (a surname, chosen by a family).
This is not the same as the plural of “fly.” The surname is a proper noun and follows its own spelling rules. In all other contexts, use flies.
Common Mistakes and How to Fix Them
✗ Incorrect: There were dozens of flys in the barn.
✓ Correct: There were dozens of flies in the barn.
Why: The plural of the noun “fly” is “flies,” following the consonant + y → ies rule.
✗ Incorrect: The bird flys across the sky every morning.
✓ Correct: The bird flies across the sky every morning.
Why: For 3rd person singular present tense of the verb “fly,” you use “flies,” not “flys.”
✗ Incorrect: She brought her fishing rod and some flys to the river.
✓ Correct: She brought her fishing rod and some flies to the river.
Why: In fly fishing, the plural of “fly” (the artificial lure) is “flies.”
The Y-to-IES Memory Trick
Whenever you see a word ending in consonant + y, think of words you already know that follow the same pattern:
Words that rhyme or follow the same rule: flies, tries, cries, spies, pies, ties, dies, dries. All of these end in “ies” — not “ys”. Your brain will recognize the pattern from words you use every day.
Test yourself: You know that “try → tries” and “spy → spies,” right? So “fly → flies” follows the exact same rule.
Fly in Different Tenses
To see when you use “flies” vs. other forms of the verb “fly”, look at this conjugation table:
| Tense | Form | Example |
|---|---|---|
| Present (I/you/we/they) | fly | I fly to Paris every summer. They fly together. |
| Present (he/she/it) | flies | She flies to Paris every summer. It flies away. |
| Past | flew | I flew to Paris last summer. |
| Past participle | flown | I have flown to Paris many times. |
| Present participle | flying | I am flying to Paris tomorrow. |
Notice: “Flies” appears only in the present tense when the subject is 3rd person singular (he, she, it, or a singular noun like “the bird” or “the pilot”).
Sample Dialogue
Leo (student): I wrote “The eagle flys over the valley.” Is that right?
Teacher: Change “flys” to “flies.” For 3rd person singular present tense, you use “flies,” not “flys.”
Leo: But the subject is singular, so I thought I’d add an ‘s’, not change the y.
Teacher: That’s a great thought, but English has a special rule: when a word ends in consonant + y, you change the y to ies for the plural or 3rd person singular. Think of “try → tries” or “spy → spies.”
Leo: Oh, I see the pattern now. So “fly → flies” follows the same rule?
Teacher: Exactly. Flies, tries, cries, spies — all the same pattern.
Quick Quiz
- What is the plural of “fly” (the insect)? Answer: Flies.
- Correct the sentence: “The bird flys south in winter.” Answer: The bird flies south in winter.
- What rule explains why “fly” becomes “flies”? Answer: The consonant + y → ies rule (like try → tries, spy → spies).
- Complete: “She _______ her kite every afternoon.” (fly/flies) Answer: Flies (3rd person singular present tense).
- Is “flys” ever correct in standard English? Answer: No, not for plurals or verb forms (except possibly as a proper noun/name).
Answers: 1. Flies · 2. Flies ✓ · 3. Consonant + y → ies · 4. Flies · 5. No, not in standard English.
Related Articles
- ↑ Master Pillar: English Grammar
- Bar Graph vs. Histogram: Understand the Difference — another confused pair
- Layed or Laid: Which Is Correct? — past tense confusion
- ↑ Back to pillar: English Confused Words (Pillar)
Frequently Asked Questions
Is “flys” ever correct?
Not in standard English. The plural of “fly” and the 3rd person singular present tense of the verb are both “flies.” The only exception would be if “Flys” is someone’s proper name or a brand name deliberately using that spelling — but that’s not a grammar rule; it’s a proper noun.
Why does “fly” become “flies” instead of “flys”?
English has a rule: words ending in a consonant followed by “y” change the “y” to “ies” for plurals and 3rd person singular verbs. Since “fly” ends in l (consonant) + y, it becomes “flies.” This is the same rule that makes “try → tries,” “spy → spies,” and “baby → babies.”
How do I know if a word ending in y should become -ies or -ys?
Look at the letter before the “y.” If it’s a consonant (like the “l” in “fly”), change y to ies (flies). If it’s a vowel (like the “o” in “boy”), just add s (boys). No change to the y is needed for vowel + y words.
Is “flies” used as both noun and verb?
Yes. “Flies” can be the plural of the noun “fly” (insects or fishing lures): “I saw three flies on the wall.” It can also be the 3rd person singular present tense of the verb “fly”: “She flies to Paris every month.” Context makes the meaning clear.
What’s the difference between “the bird flies” and “the birds fly”?
“The bird flies” uses “flies” because “bird” is singular (3rd person singular), requiring the -s form of the verb. “The birds fly” uses “fly” because “birds” is plural, so the base form is used. This is standard verb conjugation in English.
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