Deeply forked, long tail. The plumage of each sex is similar, making it dificult to distinguish between the two. Barn swallows prefer to eat flies from the insect order Diptera as well as other flying insects. These insects constitute 98.8 percent of their diet. Barn swallows are able to feed their young on the fly.
Copulation often occurs on the wing.
The nest, which is built by both parents, is a cup of mud pellets lined with grass and feathers, built on ledges of wood or rock, located in caves, along cliffs, or in buildings. The female lays about 4 or 5 eggs and the incubation period lasts 15 to 17 days. Parents share many of the duties involved while eggs are in the incubation period. Young leave the nest after 18 to 23 days. Barn swallows aggressively defend their territory from other birds.