Third instars of Macrodactylus mexicanus Burmeister, Macrodactylus nigripes Bates, and Macrodactylus ocreatus Bates are described from specimens collected from soil in corn fields at Chignahuapan, Puebla and La Malinche, Tlaxcala, and from soil in an amaranth grain field at Zapotitlán Salinas, Puebla. Illustrations of diagnostic structures, comparative comments with similar species, and a key to known third instars of Macrodactylus Dejean in Mexico are included. Data on the habits and reproductive behavior of M. ocreatus in nature and in captivity are also provided.