Red-billed quelea closely related to the fodies ("Foudia"), a genus of six or seven species that occur on the islands of the western Indian Ocean. These two genera are in turn the sister clade to the Asian species of the genus "Ploceus". The following tree represents current insight of the relationships between the species of "Quelea", and their closest relatives. Interbreeding between red-billed and red-headed queleas has been observed in captivity. The red-billed quelea is a small sparrow-like bird, approximately long and weighing , with a heavy, cone-shaped bill, which is red (in females outside the breeding season and males) or orange
Red-billed quelea quelea needs of precipitation to breed, with nest building usually commencing four to nine weeks after the onset of the rains. Nests are usually built in stands of thorny trees such as umbrella thorn acacia ("Vachellia tortilis"), blackthorn ("Senegalia mellifera") and sicklebush ("Dichrostachys cinerea"), but sometimes in sugar cane fields or reeds. Colonies can consist of millions of nests, in densities of 30,000 per ha (12,000 per acre). Over 6000 nests in a single tree have been counted. At Malilangwe in Zimbabwe one colony was long and wide. In southern Africa, suitable branches are stripped of leaves a few days