Back in England, Hopley became increasingly interested in reptiles and amphibians. She worked in the Gardens of the London Zoological Society (the precursor to today's London Zoo), and published short notes on snakes, fish, and insects in journals. Her 1882 book Snakes: Curiosities and Wonders of Serpent Life was the first popular book on snakes in English. The British Quarterly Review described Snakes as "the most thorough, the most complete, and the most popularly readable that has been published in English on the subject." Snakes includes detailed observation of feeding behaviour in snakes, including the mechanism by which Xenodon snakes erect their teeth in a viper-like fashion, an observation that predates those by E. G. Boulenger (generally credited with the description) by over 30 years.
