Description, illustrations and habitat characteristics are given for the previously unknown larva of the eastern palaearctic species Protanyderus stackelbergi (Diptera: Tanyderidae). The larva was found in a Populus leaf “pack”, a habitat not reported previously for the family, in a small stream (braid) of a larger river in Mongolia. Characters of the larval stages of Protanyderus stackelbergi and Protoplasa fitchii are compared and differences between these two genera are discussed.