Thomas was born ca. 1882 in South Kensington (1901 census) the son of Thomas Caddick Grosvenor and Emily Elizabeth A (nee Boult). His father was a chemist.

In the book 'Sunlight and Blue Shadow' pg. 41, he is mentioned :
One of Edgar's companions was a naturalist by profession, Grosvenor by name and he was mentioned as being 'a big pot in the insect line in England, an authority of bee keeping' and 'a regular contributor to the South Kensington Museum'