Flys or flies?

Flies is the plural form of the noun fly and a present tense form of the verb fly. Flys is a spelling variant of flies when citing plural one-horse carriages.

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What is the difference between flys and flies?

Like many English terms, the meaning of “fly” depends on its word form. Something can be “fly” (adjective), “fly” in the air (verb), or be a little “fly” insect (noun). But if you’re describing several “fly” or “flying” in the present tense, “flys” is never the correct word to use. 

Yes, we hate to break it to you. But nothing “flys” through the air. They either “flew” (past tense), “fly” or “flies” (present tense), have “flown” (past participle), or they are “flying” (present participle). 

Likewise, “flies” is the correct plural form for multiple flying insects–– not “flys.” You can watch a “fly” (singular) as it “flies” (plural) around, or you can watch the “flies” (plural) “fly” around (singular). 

If this common spelling error looks familiar, that’s because The Word Counter recently covered a topic of “flyer vs. flier,” where “flier” is the American English version of British English “flyer.” However, “flys” is technically a British spelling variant of “flies,” but only in the historical context of one-horse hackney carriages.  

Why use flies instead of flys?

Regular English nouns end their plural forms with an -s or -es, so it’s natural to assume the plural noun is “flys.” However, “fly” (pronounced ‘flī’) is an irregular noun, so its plural form replaces the -y with -ies: “flies.”

The same pattern occurs with irregular nouns like “lady” (ladies), “baby” (babies), or “city” (cities). But not all y-nouns use -ies for their plural forms. For instance, the plural form of “boy” is “boys,” and the plural form of “toy” is simply “toys.” 

When to tell the difference between regular and irregular forms?

Singular nouns that use a vowel (A, E, I, O, U) before the -y maintain their regular noun structure for the plural form. For example, 

  • Essay (singular) = essays (plural)
  • Birthday (singular) = birthdays (plural)
  • Valley (singular) = valleys (plural)

Singular nouns with a consonant before the -y end with -ies for the plural forms. For example, 

  • Theory (singular) = theories (plural)
  • Poppy (singular) = poppies (plural)
  • Beauty (singular) = beauties (plural) 

When to use the verb flies?

English uses “flies” for third-person singular “he,” “she,” or “it” in the present tense. This practice is fairly standard for the present tense, and you may recognize the conjugation pattern below: 

  • Singular first-person: “I fly.”
  • Singular second-person: “You fly.” 
  • Singular third-person: “He flies, “she flies,” or “it flies.”
  • Singular third-person gender-neutral: “They fly.” 
  • Plural first-person: “We fly.”
  • Plural third-person: “They fly.”

English does not use “flies” as a verb for any tense beside the present. For all other tenses, we use the following verb forms: 

  • Flew (simple past tense): “She flew.”
  • Fly (future tense): “He will fly.”
  • Flying (present participle): “You are flying.”
  • Flown (past participle): “We have flown.” 

What does flies mean as a verb?

According to the New Oxford English Dictionary, present-tense “flies” has five primary definitions (“Fly” 669). The most predominant use of the verb refers to a winged creature (such as a bird or insect) or an aircraft that travels through the air. Sentence examples include, 

  • “The bird flies to the south lawn for food.” 
  • “Dad flies to New York every summer.” 

In a similar fashion, the verb “flies” also describes something that waves or flutters in the air (such as a flag). For example, 

  • “The flag seemingly flies when there’s a little wind.” 


Aviates, cruises, drifts, glides, flutters, hangs, hovers, jets, migrates, orbits, planes, rockets, stoops, soars, wafts, or wings. 

To move quickly or escape

Plural “flies” can also describe a person or thing that flees or escapes an area in haste or moves quickly in a direction (whether willingly or by force). Similarly, one might say “time flies” to describe how quickly time escapes or passes by. 

Sentence examples:

  • “When the mad queen shouts, the window flies open.” 
  • “Whenever there’s a loud noise, the cat flies across the room to hide.”
  • “Time flies when you’re having fun.”


Barrels, beelines, blasts, bolts, chases, darts, dashes, eludes, escapes, evades, flees, hurries, jets, retreats, runs, rushes, scurries, shoots, skedaddles, travels, whisks, zips, zooms. 

Fly-ball (baseball)

In the game of baseball, “fly” is short for a “fly ball,” so we use present “flies” to describe how a fly ball hit into the air. For example, 

  • “Tony always flies to the left.”

This particular definition of “fly” is noteworthy because it’s the only time when “flied” is the correct past-tense form over the standard “flew” (669).  

Misc. meanings

Last but not least, you may read the use of “flies” in reference to a flag displayed on a pole or when someone or something is successful or accepted (informal). For example, 

  • “After a tragedy, the capitol flies the flag at half-mast.” 
  • “Anything flies when dad is babysitting.”

Synonyms for the latter sense include “holds up,” “passes,” and “washes,” which occur in phrases like “holds water” or “passes muster” (‘to withstand scrutiny’ or ‘gain acceptance’).  

What does flies mean as a noun?

The most common definition of “fly,” or plural “flies,” involves flying insects of the Order Diptera, although English speakers generally attribute the noun to any winged insect. Sentence examples include,

  • “We use sticky tape to catch invading flies.”
  • “There is a swarm of flies in the trash can.” 
  • “The buzzing sound of flies is unmistakable.”  

The noun’s secondary meaning derives from British English, where “fly” or “flies” references the openings of garments that are covered and fastened by a flap, zipper, button, or string. For instance, you might hear someone say, “Your fly is open,” meaning the zipper of your pants is undone. 

The least common use of the plural noun occurs with “the flies,” a phrase that references “the space over the stage in a theater” (“Fly” 669). For example, 

  • “The actor descended from the flies.” 

Is fly an adjective?

Fly” is an informal adjective that describes a noun as “stylish and fashionable” or “knowing and clever,” although “flys” or “flies” do not apply to this form. For example, 

  • “He thinks he’s so fly.” 
  • “Strangers would compliment her ‘fly’ aesthetic.” 

Are fly insects the same as fireflies or butterflies?

Modern English speakers often use “fly” or “flies” to reference any flying insect with a darkly-colored thorax, wings, suckling mouthparts, and six legs (“hexapoda”). However, there are many flying insects we associate with “fly” that are not flies at all, such as: 

  • Firefly 
  • Mayfly 
  • Sawfly
  • Butterfly
  • Hanging fly and scorpionfly 
  • Alderfly, dobsonfly, and fishfly 
  • Dragonfly and damselfly 
  • Stonefly 
  • Snakefly
  • Caddisfly

As we can see, there are many insects with a “fly” name, but the only “true flies” descend from the order Diptera (the same confusion occurs with “bunny vs. rabbit”). Their similarities in phenotype exist because they are distantly related through a common ancestor in the early Devonian period–– back before the origin of trees. 

In fact, dragonfly and damselfly species predate the dinosaurs and primate evolutions by millions of years. Meanwhile, all moth, butterfly, and subsequent Dipteran lineages evolved from relatives of the Odonata during the Permian to Jurassic periods, which is still impressively ancient. 

What are common examples of “true flies”?

Fruit fly (family Trypetidae and Drosophilidae)

Fruit flies (or “vinegar flies” of the Drosophila) are among the most common kitchen flies, as they enjoy sweet and fermented liquids found in our kitchen or dining area. 

Bluebottle fly (family Calliphoridae)

Also known as a “blowfly,” bluebottle flies are large fly species that often have a shiny blue or green appearance. They are known to congregate around rotting waste, where their larvae develop inside dead animals. 

Housefly (family Muscidae)

Particularly known for their white maggots (larvae), common house flies are the large, greyish flies that congregate and lay eggs on garbage and animal feces. Houseflies (specifically Musca domestica) pose a risk to human health because they regurgitate solid food to produce a consumable liquid–– and often on the surfaces of your everyday surroundings. 

Flesh fly (family Sarcophagidae)

Larger than most houseflies, flesh flies are also attracted to rotting carcasses (hence the name). Flesh flies are distinguishable from houseflies by the checkerboard pattern on their abdomen. 

Stable fly (Stomoxys calcitrans)

If a large fly is biting your ankles, it might be a stable fly. Both male and female stable flies bite animals and humans to consume their blood, although researchers deny any indication of disease transmission. 

Cluster fly (Pollenia rudis)

Cluster flies are large, fuzzy pests that invade warm attics in the fall to hibernate. But instead of integrating waste into their life cycles, they deposit eggs on earthworms, where their larvae later consume the worm’s body. 

Drainfly (family Psychodidae)

Drain flies or “sewer flies” are small flies found in restrooms that look similar to moths. These particular flies are attracted to restrooms because they lay larvae in accumulating muck found in sink and toilet drains. 

Horse fly (family Tabanus)

Horseflies are larger outdoor flies characterized by their brown hue, bee-like flying techniques, and their tendency to bite (it’s quite annoying, actually). 

Sand fly (family Phlebotominae)

Sandflies live near beaches, rivers, and lakes because they reproduce in aquatic environments. They are notorious for their biting behavior, which has led to viral and protozoan parasite diseases. 

Are mosquitos and fungus gnats flies?

While they lack the “fly” in their name, mosquitos and fungus gnats are common true flies. Gardeners often associate fungus gnats (family Sciaridae and Mycetophilidae) as a sign of trouble, as the mosquito-like insect lays larvae in moist environments with fungi, their primary food source. 

However, true mosquitos (family Culicidae) are unmistakable for their predatory bites that leave victims with itchy sores and, sometimes, disease. As noted by the Encyclopedia Britannica, these bloodsuckers are vectors for illnesses such as dengue, encephalitis, filariasis, malaria, yellow fever, and Zika fever. 

Test Yourself!

Before you fly off to your next writing assignment, test how well you understand “flys” vs. “flies” with the following multiple-choice questions. 

  1. Flys is the plural of fly when it means ______________.
    a. Flying Dipteran insects 
    b. One-horse hackney carriages
    c. Clever and stylish persons or things
    d. A fly-ball
  2. Which answer does not relate to the plural noun flies
    a. Flying insects
    b. A quick movement from an area of land
    c. Pant zippers
    d. Theater stages
  3. Which is a present tense conjugation of the verb fly? 
    a. Fly
    b. Flies
    c. Flying
    d. A and B
  4. Choose the correct present tense form: “The girl’s cat flies through the air.”
    a. Flew
    b. Flys
    c. Flies
    d. Flyed
  5. Which of the following flying insects is not a true fly?
    a. Horsefly
    b. Fungus Gnat
    c. Sawfly 
    d. Mosquito
  6. [Bonus] Choose the correct verb form: “Jaime ________ the aeroplane back to Wales every spring.” 
    a. Flies
    b. Flew
    c. Fly
    d. A and B


  1. B
  2. B
  3. D
  4. C
  5. C
  6. D


  1. Cranshaw, W.S., and Fb. Peairs. “Common Flies Found in Buildings.” Home and Garden Series, Colorado State University Extension, 2021. 
  2. Editors of Encyclopaedia Britannica, The. “Horse fly.” Encyclopædia Britannica,, 7 Apr 2017. 
  3. Editors of Encyclopaedia Britannica, The. “Mosquito.” Encyclopædia Britannica,, 2 June 2020. 
  4. Editors of Encyclopaedia Britannica, The. “Sand fly.” Encyclopædia Britannica,, 11 Sept 2008.
  5. Flies.” The Thesaurus, Merriam-Webster Inc., 2021.
  6. “Fly.” The New Oxford American Dictionary, 3rd ed., Oxford University Press, 2010, p. 669.
  7. Fly.” The American Heritage Dictionary of the English Language, 5th ed., Houghton Mifflin Harcourt Publishing Company, 2020. 
  8. Fly.” Reverso Conjugator, Reverso-Softissimo, 2021. 
  9. Misof, B et al. “Phylogenomics resolves the timing and pattern of insect evolution.” Science, Research Gate, Nov 2014. 
  10. Prevention and Control: The House Fly and Other Filth Flies.” Illinois Department of Public Health, University of Illinois Extension, n.d.