The distribution and host associations of the ceratophyllid flea, Tarsopsylla octodecimdentata (Kolenati, 1863), are discussed. Tarsopsylla o. coloradensis (Baker, 1895) is synonymized with the nominate taxon on the grounds that the slight variations in the only anatomical feature distinguishing the two taxa, the contours of the seventh sternum in the females, is insufficient to justify their separation. The species is distributed from Great Britain, east to the western region of North America. It is a parasite of squirrels belonging to the genera Sciurus Linnaeus, 1758, Tamiasciurus Trouessart, 1880, and Glaucomys Thomas, 1908. Judging from the lack of a metapleural arch it is thought to be a “nest flea.”