Born in Taunton, Somerset, England,[1] the son of Reverend W. R. Crotch, he became interested in insects in his childhood.

In 1873 he accepted a position as assistant from Louis Agassiz at the Harvard Museum of Comparative Zoology with Hermann August Hagen.

He made collections of Coleoptera and Lepidoptera during 1873 in California, Oregon, and Vancouver Island, as well as various areas of south-central British Columbia.

[4] Crotch was the author of a number of books, including Checklist of the Coleoptera of America (1873) and A revision of the Coleopterous family Coccinellidae (1874).

He corresponded with Charles Darwin who wrote:[6] I am greatly indebted to Mr G. R. Crotch for having sent me numerous prepared specimens of various beetles belonging to these three families [Crioceridae, Chrysomelidae, Tenebrionidae] and others, as well as for valuable information of all kinds ...