Miriam Rothschild was born in 1908 in Ashton Wold, near Oundle in Northamptonshire, the daughter of Charles Rothschild of the famous Rothschild family of Jewish bankers and Rozsika Edle Rothschild (née von Wertheimstein), a Hungarian sportswoman. Her brother was Victor Rothschild, 3rd Baron Rothschild and her sister Kathleen Annie Pannonica Rothschild (Baroness Nica de Koenigswarter) would later be a bebop jazz enthusiast and patroness of Thelonious Monk and Charlie Parker.
Miriam's father had described 500 new species of flea, and her uncle Lionel Walter Rothschild had built a private natural history museum at Tring. By the age of 4 she had started collecting ladybirds and caterpillars and taking a tame quail to bed with her.
World War I broke on the eve of Miriam's sixth birthday in 1914, while the Rothschilds were holidaying in Austro-Hungary. They hurried home on the first westward train but, unable to pay, had to borrow money from a Hungarian passenger who commented "This is the proudest moment of my life. Never did I think that I should be asked to lend money to a Rothschild!"
Her father died when she was 15 and she became closer to her uncle. She received no formal education before the age of 17 when she demanded to go to school, but did not take a degree. A keen sportswoman, she played squash and cricket internationally.
During the 1930s she made a name for herself at the Marine Biological Station in Plymouth, studying the mollusc Nucula and its trematode parasites (Rothschild 1936, 1938a, 1938b). Because of her inherited wealth, she never had to apply for any grants or funding. As a result of this and her lack of formal education — all her doctorates were honorary — she would always be an "amateur".
Rothschild was a leading authority on fleas. She was the first person to work out the flea jumping mechanism. She also studied the flea's reproductive cycle and linked this, in rabbits, to the hormonal changes within the host. She wrote about 350 papers on entomology, zoology and other subjects.
Rothschild was known as an eccentric. She became a vegetarian, a teetotaller, eschewed make-up, and wore leather-free shoes and boots — moon-boots in winter, tennis shoes summer and white Wellington boots in the evening. She had red hair (though it later greyed), a bulky figure and wore a loose, mauve silk dress and matching kerchief — designed to "cut down on the need to make unnecessary choices". Nevertheless protective of Jews, she could not accept Judaism and was an atheist.
She was a member of the Oxford genetics school during the 1960s, and Rothshild was one of the few women with whom E.B. Ford had good acquaintances. She campaigned with Ford for the legalisation of homosexuality.
Rothschild was also the author of books on her father (Rothschild's Reserves – time and fragile nature) and her uncle (Dear Lord Rothschild).
- Rothschild, M (1936) Gigantism and variation inf Peringia ulvae Pennant 1777, caused by infection with larval trematodes. J. Mar. Biol. ASsn UK 20:537–46
- Rothschild, M (1938a) Further observations on the effect of trematode parasites on Peringia ulvae(Pennant) 1777. Novavit Zool. 41:84–102
- Rothschild, M (1938b) Observations on the growth and trematode infetions of Peringia ulvae (Penntant) 1777 in a pool in the Tamar saltings, Plymouth.