Eggs are laid one a day and there is often a second clutch. In cold weather feeding the young becomes difficult. At such times the male swallows act rather selfishly. The females spend as much time feeding their brood as they do looking after themselves. But the males put much more effort into seeing to their own needs.
Flies are certainly favourites, particularly for first broods.
Eight out of every 10 insects eaten are flies. Surprisingly, most are large including greenbottles, bluebottles and horseflies. For the first few days after the nestlings have hatched, unmated male swallows are frequent visitors to the nest. Surprisingly, one way that such males can acquire a mate is to kill the young nestlings and then pair with the female who has to start a new family. One observer watched a male remove a whole brood by picking up each nestling, flying some distance away and then dropping it on the ground.