Marjorie Guthrie was brought up in Liverpool and went to Newnham College, Cambridge, graduating in 1948. She returned to Liverpool for her PhD, for which she recorded the protozoans of salt marshes. Appointed as a lecturer in the zoology department at Leicester University, Marjorie balanced a heavy teaching load on subjects from physiology to palaeontology with continuing her ecological research at the Ferry House laboratory of the Freshwater Biological Association on Lake Windermere. She retired to the Lake District, where she wrote Animals of the Surface Film (1989). She and her husband Simon would set off with waders and collecting pots to sample remote ponds in search of water boatmen or the endangered medicinal leech. Her conservation work as a volunteer for the Cumbria Wildlife Trust was recognised in 2013 with the award of a Badger's Paw. She died in that year.