Descriptions and illustrations are given for one new species of Rallicola Johnston and Harrison, 1911 and three new species of Myrsidea Waterston, 1915 from ovenbirds, leaftossers, and woodcreepers from Costa Rica. These chewing lice and their type hosts are as follows: Rallicola (Rallicola) ochrolaemi and Myrsidea ochrolaemi ex Automolus ochrolaemus (Furnariidae: Furnariinae), Myrsidea calvi ex Sclerurus guatemalensis (Furnariidae: Scleruridae), and (Myrsidea souleyetii ex Lepidocolaptes souleyetii (Furnariidae: Dendrocolaptinae). Records of five other louse species of the genus Myrsidea, Menacanthus and Rallicola from dendrocolaptid hosts are also discussed. These are the first records of the genus Menacanthus and Myrsidea from members of the passerine subfamily Dendrocolaptinae.