I came across this in George Orwell's Homage to Catalonia
written in 1937.
The extract was written in the Sierra de Alcubierre in the Monegros on the Aragonese Front, during the spring of 1937.
The "exquisite green frogs the size of a penny" are clearly tree frogs. I'm not sure from their distribution map which species of Hyla it is, meridionalis or arborea?
Spring was really here at last. The blue in the sky was softer, the air grew suddenly balmy. The frogs were mating noisily in the ditches. Round the drinking-pool that served for the village mules I found exquisite green frogs the size of a penny, so brilliant that the young grass looked dull beside them. Peasant lads went out with buckets hunting for snails, which they roasted alive on sheets of tin.
Neither of the hyla species maps current include eastern Huesca in their distribution.
Are they inaccurate or are we talking about a local extinction?
Which species are we talking about? My guess is arborea.http://www.mma.es/portal/secciones/biodiversidad/inventarios/inb/anfibios_reptiles/pdf/anfibios_24.pdfhttp://www.mma.es/portal/secciones/biodiversidad/inventarios/inb/anfibios_reptiles/pdf/anfibios_23.pdf
I'm guessing the other frogs are perezi's "The frogs were mating noisily in the ditches"