The larva of Argas (Persicargas) keiransi Estrada-Peña, Venzal & González-Acuña n. sp. is described from specimens collected on the neck of a chimango, Milvago c. chimango (Aves: Falconiformes) in the Chillán, Chile, in the Sub-Antarctic biogeographical region. The larva of the new species shares the tarsus I setal formula with A. (P.) giganteus, these being the only two Persicargas species with three pairs of ventral setae plus both av4 and pv4 setae. However, it is unique in having a dorsal plate "V" or "U" shaped, with the anterior end open, without the typical reticulated pattern present in the remaining species of the genus.