Theo was apprenticed as a stationer and printer, eventually starting his own letterpress printing business.
(Sources: copy marriage and birth certificates from GRO) He probably lived most of his life near Regent's Park as he seems to have spent most of his time visiting the Gardens of the Zoological Society of London and producing beautiful watercolour paintings of the exhibits.
These he published as original works of art, along with printed or hand-written text, in a large number of books.
His special interest was entomology, but he also published works on molluscs, birds and mammals, including extinct ones.
This was the "first accurate history of the Zoo" and included never before published information concerning the "true story of Jumbo", the "fiasco of the white elephant" and the "fiction of the intellectually-gifted chimpanzee, Sally".