Cynthia Evelyn Longfield (16 August 1896 – 27 June 1991) was an Anglo-Irish entomologist and explorer and the first woman member of the Entomological Society. She was an expert on the dragonfly and an explorer. She was called "Madame Dragonfly" for her extensive work. She was passionately fond of dragonflies and her dominant area of interest was natural history. She travelled extensively and published The Dragonflies of the British Isles in 1937. She worked as a research associate at the Natural History Museum, London. Longfield was the expert on the dragonflies at the museum, researching particularly African species.