The Kilkenny cats are a fabled pair of cats from County Kilkenny (or Kilkenny city in particular) in Ireland, who fought each other so ferociously that only their tails remained at the end of the battle. Often the absurd implication is that they have eaten each other. In the nineteenth century the Kilkenny cats were a common simile for any conflict likely to ruin both combatants. Kilkenny cat is also used more generally for a fierce fighter or quarrelsome person. These senses are now rather dated.; In the later twentieth century the motif was reclaimed by Kilkenny people as a positive symbol of tenacity and fighting spirit, and "the Cats" is the county nickname for the Kilkenny hurling team. The original story is attested from 1807 as a simple joke or Irish bull; some early versions are set elsewhere than Kilkenny. Nevertheless, theories have been offered seeking a historical basis for the story's setting.

Versions of the story The earliest attested version of the story is from June 1807, in Anthologia, a collection of jokes and humorous pieces copied by "W.T." of Inner Temple from unnamed previous publications.; Steven Connor characterises the story as an Irish bull. Under the heading "Kilkenny Cats" it runs: In a company, consisting of naval officers, the discourse happened to turn on the ferocity of small animals; when an Irish gentleman present stated his opinion to be, that a Kilkenny cat, of all animals, was the most ferocious; and added, "I can prove my assertion, by a fact within my own knowledge:— I once," said he, "saw two of these animals fighting in a timber yard, and willing to see the result of a long battle, I drove them into a deep sawpit, and placing some boards over the mouth, left them to their amusement. Next morning I went to see the conclusion of the fight, and what d'ye think I saw?"– "One of the cats dead, probably," —replied one of the company.— "No by Ja—s! there was nothing left in the pit, but the two tails and a bit of flue!"

The tale was repeated verbatim the next month in The European Magazine'''s review of Anthologia, as well as The Sporting Magazine, also in London, and Walker's Hibernian Magazine in Dublin. It reappeared in 1812 in Thomas Tegg's The Spirit of Irish Wit, and in the 1813 supplement to William Barker Daniel's Rural Sports.

The following appears in Thomas Gilliland's The Trap, an 1808 satire on the theme of love:; quoted in When I was last at Kilkenny, said Teague, I saw two big ram-cats fight a duel for love, your honour; and they fought, and fought, till they ate each other up. Devil burn me, if I lie, your honour! I went after them into the gutter! "Tommy!" says I, "my dear Phely!" says I, but no Tommy or Phely was there: I found only the tips of their tails.

An 1811 joke book from Boston in the United States included: On a gentleman's reading an account of a tiger fight in the East Indies, an Irishman present exclaimed: 'a tiger be hang'd! Why, sir, I once myself saw two Kilkenny cats fight till they devoured each other up, excepting the very tips of their two tails.'

Another version is alluded to in an 1816 critique of a pamphlet by Andrew O'Callaghan, master of Kilkenny College: There is a story told in Kilkenny, that several cats had been locked up in a room, for a fortnight together, without food, and, upon opening the door, there was nothing found but the tail of one of them. Surely Mr. O'C. must have been dreaming of this native story, when he made his arguments thus to swallow themselves, after destroying each other—but the tail of one of them remains Responding to the 1816 critique, Rowley Lascelles, an English antiquarian based in Ireland, denied the existence of such a story, which he saw as a slur on Kilkenny.

Although in 1835 John Neal called the story "one of the oldest and most undoubted Joe [Miller]s",; reprinted in the first edition of Joe Miller's Jests to include it was in 1836 (verbatim from Anthologia). Theodore Hook's 1837 novel Jack Brag jocularly sources the story to [Joe] Miller's History of Ireland.

Elsewhere than Kilkenny An 1817 memoir of the Irish wit John Philpot Curran situates the story in Sligo rather than Kilkenny, as a tall tale told by Curran: Passing his first summer at Cheltenham ... he had resort to a story to draw himself into notice. ... The conversation of the table turning altogether on the stupid, savage, and disgusting amusement of cock-fighting, he was determined to put an end to it, by the incredible story of the Sligo cats. At [a cat-fight meeting in Sligo] three matches were fought on the first day ... and before the third of them was finished (on which bets ran very high), dinner was announced in the inn where the battle was fought. The company agreed ... to lock up the room, leaving the key in trust to Mr. Curran, who protested to God, he never was so shocked, that his head hung heavy on his shoulders, and his heart was sunk within him, on entering with the company into the room, and finding that the cats had actually eaten each other up, save some little bits of tails which were scattered round the room. The Irish part of the company saw the drift, ridicule, and impossibility of the narrative, and laughed immoderately, while the English part yawned and laughed, seeing others laugh, and sought relief in each other's countenances.

In Real life in Ireland, an 1821 stage Irish novel by Pierce Egan, Captain Grammachree, a retired soldier, tells Brian Boru, a young country squire, of a cat-fight in the neighbourhood of Dublin: 'There was hundreds betted, but not a cross won or lost; for by Jasus! they left nothing on the ground but a bunch of hair and two tails!' 'What!' said Brian, 'then I suppose the cats ran away?' 'An Irish cat run away!' sneered Grammachree, 'no; never! by the powers of Moll Kelly! they eat one another up!'

An 1830 "dialogue on Popery" by one Jacob Stanley summarises "the Travellers tale of the Irish Cat fight", giving no specific location.

The battle of the cats of Ireland S. Redmond in 1864 in Notes and Queries recounted a tale told to him "more than thirty years" earlier when he was "very young" by "a Kilkenny gentleman", about a battle "some forty years before" [i.e. about 1790] on "a plain near that ancient city": One night, in the summer time, all the cats in the city and county of Kilkenny, were absent from their "local habitations;" and next morning, the plain alluded to (I regret I have not the name) was found covered with thousands of slain tabbies; and the report was, that almost all the cats in Ireland had joined in the contest; as many of the slain had collars on their necks, which showed that they had collected from all quarters of the island. The cause of the quarrel, however, was not stated; but it seemed to have been a sort of provincial faction fight between the cats of Ulster and Leinster—probably the quadrupeds took up the quarrels of their masters, as at that period there was very ill feeling between the people of both provinces.

Although Redmond states "This has nothing to do with the story of the two famous Kilkenny cats", the two have occasionally been linked subsequently. A similar story was told in Charles Henry Ross' 1867 Book of Cats, to which Kilkenny antiquarian John G. A. Prim responded that he had heard such a story told of many places in Ireland, but not of Kilkenny. In 1863, Once A Week had a story of a similar battle in Yorkshire. Folklorist John O'Hanlon in 1898 published a version from John Kearns of Irishtown, Dublin which situated the battle on Scald Hill in Sandymount, the future site of Star of the Sea Catholic Church, witnessed by curate Father Corrigan. In the 1930s, the Irish Folklore Commission noted a seanchaí from Rossinver, County Leitrim, tell of a cat battle in Locan Dhee near Kinlough on New Year's Day 1855.

Use as a simile

The story was sufficiently well known in the 19th century to be used frequently as a simile for "combatants who fight until they annihilate each other"; to "fight like [the] Kilkenny cats" means "to engage in a mutually destructive struggle". Early instances include: (from 1814) an account in Niles' Register of the loss of USS Wasp after sinking HMS Avon; (from 1816) the critique of Andrew O'Callaghan mentioned earlier; a letter from the 4th Duke of Buccleuch to Walter Scott comparing Lord Byron's poem "Darkness" to the story; and a riposte to disagreeing literary critics: Indeed, so mortal is your reciprocal hostility, that your victims may, with Mercutio, form the reasonable expectation, that, being, 'two such, we shall have none shortly, for one will kill the other;' and like the celebrated Kilkenny cats, leave no other vestige to designate the tribe of ferae naturae to which you belong, than an odd tooth or a claw!

One context for the simile was advocating isolationism, allowing one's enemies to defeat each other, or a divide-and-conquer policy. A report in Niles' Register of Spanish church opposition to the 1817 tax reform of wished 'the fate of the "Kilkenny cats"' on "Ferdinand and his priests". Similarly Charles Napier in 1823 hoped "the French and Spaniards [would] war like Kilkenny cats"; likewise Figaro in London in 1832 urging British neutrality after the Ten Days' Campaign and Charles Darwin in 1833 in Buenos Aires during the Revolution of the Restorers. J. S. Pughe in a 1904 political cartoon in Puck depicted Japan and Russia as Kilkenny cats fighting the Russo-Japanese War in Manchuria. Similarly in 1941, after Germany invaded the Soviet Union, Clifford Berryman depicted Adolf Hitler and Joseph Stalin as "a modern version of the Kilkenny Cats". In The German Ideology, Karl Marx and Friedrich Engels accuse Bruno Bauer of fomenting antagonism between Max Stirner and Ludwig Feuerbach "as the two Kilkenny cats in Ireland".

Conversely, the fable serves as a cautionary tale for the moral "united we stand, divided we fall". It was invoked in 1827, in The Lancet during disputes around the Royal College of Physicians; and in The Literary Gazette of the rivalry between Drury Lane and Covent Garden theatres. It was a common metaphor before and during the American Civil War, a conflict seen as likely to destroy both sides; especially when criticising the war of attrition strategy of Ulysses S. Grant. Some extended the metaphor to say the North would win as having the longest tail; this was popularly reported in 1864 as a quip by Grant, but George Gordon Meade made the same comparison in an 1861 letter to his wife. Some Mormons viewed the Civil War as fulfilling a prophecy by founder Joseph Smith, who said after an 1843 attempt to arrest him, "The constitution of the United States declares that the privilege of the writ of habeas corpus shall not be denied. Deny me the writ of habeas corpus, and I will fight with gun, sword, cannon, whirlwind, and thunder, until they are used up like the Kilkenny cats." Donald Dewar, the then First Minister of Scotland, in 1999 denied media talk of a rift with John Reid, the Scottish Secretary, conceding, "I must confess the casual outsider who simply read the headlines might think it was a collection of Kilkenny cats fighting". In the Supreme Court of India in December 2018, K. K. Venugopal, the Attorney General, justified the government's suspension of Alok Verma and Rakesh Asthana from the Central Bureau of Investigation by saying, "The government was watching with amazement the director and his deputy fight like Kilkenny cats." Indian media explained the simile in their reports on the case.