High Quality Content by WIKIPEDIA articles! The Formicariidae, formicariids, or ground antbirds are a family of smallish passerine birds of subtropical and tropical Central and South America. They are between 10 and 20 cm (4–8 in) in length, and are related to the antbirds, Thamnophilidae, and gnateaters, Conopophagidae. This family contains probably (see below) some 100–120 species in 1 or 2 large and a number of fairly small genera.