It builds a cup nest from mud pellets in barns or similar structures and feeds on insects caught in flight.

There are frequent cultural references to the barn swallow in literary and religious works due to both its living in close proximity to humans and its annual migration.

[6] The female is similar in appearance to the male, but the tail streamers are shorter, the blue of the upperparts and breast band is less glossy, and the underparts paler.

[11] The barn swallow was described by Carl Linnaeus in his 1758 10th edition of Systema Naturae as Hirundo rustica, characterised as "H. rectricibus, exceptis duabus intermediis, macula alba notatîs".

[14][7] The Oxford English Dictionary dates the English common name "barn swallow" to 1851,[15] though an earlier instance of the collocation in an English-language context is in Gilbert White's popular book The Natural History of Selborne, originally published in 1789: The swallow, though called the chimney-swallow, by no means builds altogether in chimnies [sic], but often within barns and out-houses against the rafters ...

There are few taxonomic problems within the genus, but the red-chested swallow—a resident of West Africa, the Congo Basin, and Ethiopia—was formerly treated as a subspecies of barn swallow.

The red-chested swallow is slightly smaller than its migratory relative, has a narrower blue breast-band, and (in the adult) has shorter tail streamers.

In eastern Asia, a number of additional or alternative forms have been proposed, including saturata by Robert Ridgway in 1883,[17] kamtschatica by Benedykt Dybowski in 1883,[18] ambigua by Erwin Stresemann[19] and mandschurica by Wilhelm Meise in 1934.

The presence of accessible open structures such as barns, stables, or culverts to provide nesting sites, and exposed locations such as wires, roof ridges or bare branches for perching, are also important in the bird's selection of its breeding range.

[38] It is most common in open, low vegetation habitats, such as savanna and ranch land, and in Venezuela, South Africa and Trinidad and Tobago it is described as being particularly attracted to burnt or harvested sugarcane fields and the waste from the cane.

[41] Individual birds tend to return to the same wintering locality each year[42] and congregate from a large area to roost in reed beds.

The barn swallow has been recorded as breeding in the more temperate parts of its winter range, such as the mountains of Thailand and in central Argentina.

[7][44] Migration of barn swallows between Britain and South Africa was first established on 23 December 1912 when a bird that had been ringed by James Masefield at a nest in Staffordshire, was found in Natal.

[45] As would be expected for a long-distance migrant, this bird has occurred as a vagrant to such distant areas as Hawaii, Bermuda, Greenland, Tristan da Cunha, the Falkland Islands,[7] and even Antarctica.

In the northern part of the range, it usually starts late May to early June and ends the same time as the breeding season of the southernmost birds.

[7] Once established, pairs stay together to breed for life, but extra-pair copulation is common, making this species genetically polygamous, despite being socially monogamous.

It is constructed by both sexes, although more often by the female, with mud pellets collected in their beaks and lined with grasses, feathers, algae[67] or other soft materials.

[7] Barn swallow nestlings have prominent red gapes, a feature shown to induce feeding by parent birds.

[78] The barn swallow has an enormous range, with an estimated global extent of about 250,000,000 km2 (97,000,000 sq mi) and a population of 190 million individuals.

[37] This is a species that has greatly benefited historically from forest clearance, which has created the open habitats it prefers, and from human habitation, which have given it an abundance of safe man-made nest sites.

However, there has been an increase in the population in North America during the 20th century with the greater availability of nesting sites and subsequent range expansion, including the colonisation of northern Alberta.

[7] A specific threat to wintering birds from the European populations is the transformation by the South African government of a light aircraft runway near Durban into an international airport for the 2010 FIFA World Cup.

[79][80] However, following detailed evaluation, advanced radar technology will be installed to enable planes using the airport to be warned of bird movements and, if necessary, take appropriate measures to avoid the flocks.

[39] Climate change may affect the barn swallow; drought causes weight loss and slow feather regrowth, and the expansion of the Sahara will make it a more formidable obstacle for migrating European birds.

Conversely, warmer springs may lengthen the breeding season and result in more chicks, and the opportunity to use nest sites outside buildings in the north of the range might also lead to more offspring.

[61] The barn swallow is an attractive bird that feeds on flying insects and has therefore been tolerated by humans when it shares their buildings for nesting.

An early reference is in Virgil's Georgics (29 BC), "Ante garrula quam tignis nidum suspendat hirundo" (Before the twittering swallow hangs its nest from the rafters).

[82] Many cattle farmers believed that swallows spread Salmonella infections; however, a study in Sweden showed no evidence of the birds being reservoirs of the bacteria.

In his poem "The Waste Land", T. S. Eliot quoted the line "Quando fiam uti chelidon [ut tacere desinam]?"

[84] Gilbert White studied the barn swallow in detail in his pioneering work The Natural History of Selborne, but even this careful observer was uncertain whether it migrated or hibernated in winter.