Musca (Latin for 'the fly') is a small constellation in the deep southern sky. It was one of 12 constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman, and it first appeared on a celestial globe 35 cm (14 in) in diameter published in 1597 (or 1598) in Amsterdam by Plancius and Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in Johann Bayer's Uranometria of 1603. It was also known as Apis (Latin for 'the bee') for 200 years. Musca remains below the horizon for most Northern Hemisphere observers.

Many of the constellation's brighter stars are members of the Scorpius–Centaurus association, a loose group of hot blue-white stars that appears to share a common origin and motion across the Milky Way. These include Alpha, Beta, Gamma, Zeta² and (probably) Eta Muscae, as well as HD 100546, a blue-white Herbig Ae/Be star that is surrounded by a complex debris disk containing a large planet or brown dwarf and possible protoplanet. Two further star systems have been found to have planets. The constellation also contains two cepheid variables visible to the naked eye. Theta Muscae is a triple star system, the brightest member of which is a Wolf–Rayet star.

Musca was one of the 12 constellations established by the astronomer Petrus Plancius from the observations of the southern sky by the Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman, who had sailed on the first Dutch trading expedition, known as the Eerste Schipvaart, to the East Indies. De Houtman included it in his southern star catalogue in 1598 under the Dutch name De Vlieghe, "The Fly". They assigned four stars to the constellation, with a star that would be later designated as Beta Muscae marking the head, Gamma the body, and Alpha and Delta the left and right wings, respectively. It first appeared on a 35-cm-diameter (14-in) celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius, though was unnamed. The first depiction of this constellation in a celestial atlas was in the German cartographer Johann Bayer's Uranometria of 1603, though Bayer termed it Apis— "the Bee", a name by which it was known for the next two centuries. A 1603 celestial globe by Willem Blaeu depicts it as providing nourishment for the nearby constellation Chamaeleon—its tongue trying to catch the insect.

The French explorer and astronomer Nicolas Louis de Lacaille called it la Mouche on the 1756 version of his planisphere of the southern skies. Jean Fortin retained the French name in 1776 for his Atlas Céleste, while Lacaille Latinised the name for his revised Coelum Australe Stelliferum in 1763. Lacaille renamed it to Musca Australis, the Southern Fly—Australis, since it counterparted the now discarded constellation of Musca Borealis composed of a few stars in Aries, and to avoid confusion with Apus. Today, the name is simply Musca. It is the only official constellation depicting an insect.

The Kalapalo people of Mato Grosso state in Brazil called Alpha and Beta Muscae (along with Beta and Kappa Crucis) Kutsu anangagï "Ornate Hawk-Eagle's double flutes". The Wardaman people of the Northern Territory in Australia perceived the main stars of Musca as a ceremonial boomerang, part of the Central Arena—a sacred area surrounding the constellation Crux that depicts the lightning creation beings and where they teach Wardaman customs; Alpha and Beta also signified a ceremonial headband, while Gamma and Delta represented two armbands. In central Australia, the Arrernte and Luritja peoples living in on a mission in Hermannsburg viewed the sky as divided between them, east of the Milky Way representing Arrernte camps and west denoting Luritja camps. The stars of Musca, along with Fomalhaut, Alpha Pavonis, and Alpha and Beta Gruis, were all claimed by the Arrernte.

Musca is bordered by Crux to the north, Carina to the west, Chamaeleon to the south, Apus and Circinus to the east, and Centaurus to the northeast. Covering 138 square degrees and 0.335% of the night sky, it ranks 77th of the 88 constellations in size. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Mus". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of six segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 11^h 19.3^m and 13^h 51.1^m , while the declination coordinates are between −64.64° and −75.68°. The whole constellation is visible to observers south of latitude 14°N.

Lacaille charted and designated 10 stars with the Bayer designations Alpha to Kappa in 1756. He catalogued stars that became Lambda and Mu, but did not designate them as he considered them informes as they lay outside the asterism proper. Francis Baily considered them part of Musca, and Gould gave them their Bayer designations. Baily also dropped Kappa, which he felt was too faint to warrant a name, and designated two adjacent stars as Zeta¹ and Zeta². These last two stars are 1° apart, quite far to be sharing a Bayer designation. Lacaille had originally labelled the fainter one as Zeta, while Baily presupposed he had meant to label the brighter one. Reluctant to remove Lacaille's designation, he gave them both the Zeta designation. Altogether there are 62 stars brighter than magnitude 6.5 in the constellation.

The pattern of the brightest stars resembles that of Ursa Minor, in that the stars form a pattern reminiscent of a bowl with a handle. Lying south-southeast of Acrux in neighbouring Crux is Alpha Muscae. It is the brightest star in the constellation with an apparent magnitude of 2.7. Lying around 310 light-years away, it is a blue-white star of spectral type B2IV-V that is around 4520 times as luminous and 8 times as massive as the Sun. The star is a Beta Cephei variable with about 4.7 times the Sun's diameter, and pulsates every 2.2 hours, varying by 1% in brightness. A nearby star of magnitude 13 may or may not be a companion star. Marking the fly's tail is Gamma Muscae, a blue-white star of spectral type B5V that varies between magnitudes 3.84 and 3.86 over a period of 2.7 days. It is a variable of a different type, classed as a slowly pulsating B star, a type of variable. It is around five times as massive as the Sun.