Although he may not have paid £1,000 for a flea in 1914 (about $135,000 today), the banker Charles Rothschild was in fact a respected entomologist and an avid collector of fleas. He acquired some 260,000 specimens, including about 500 new species that he discovered, all of which are now part of the Siphonaptera collection in the British Natural History Museum. His daughter Miriam followed in his footsteps; her catalog of his collection (in collaboration with G. H. E. Hopkins) is considered a tour de force, and her book on parasites, Fleas, Flukes and Cuckoos, was a popular success. She was the first person to discern and describe the flea’s jumping mechanism.

(Sources here, here, and here)