One of a handful of northeast Brazilian endemics considered Critically Endangered by BirdLife International, the Alagoas Antwren was described as recently as the mid 1980s, as a subspecies of the southeast Brazilian endemic, the Unicolored Antwren (Myrmotherula unicolor). Males of the two differ only mensurally, and females in being more rufescent below, although the songs of the two species differ more obviously. This antwren originally was discovered above the small town of Murici, in the state of Alagoas, but subsequently has been found only in the neighboring state of Pernambuco, where it is now known from four localities, one of them only very recently discovered. It forages in pairs and within small mixed-species flocks in the middle strata of upland semi-humid forest, and these flocks reportedly also regularly include White-flanked Antwrens (Myrmotherula axillaris) and a variety of other insectivores. The diet of the Alagoas Antwren consists of arthropods, and breeding probably occurs in February.