The year is established by the relationship between this letter and CD’s notes on Orchis maculata dated 20 June 1862 (see n. 2, below).

In a note dated 20 June 1862 (DAR 70: 12–14), CD recorded that his son George Howard Darwin had caught six flies (Empis lucida) with pollinia of Orchis maculata attached to their eyes, as well as one specimen of E. pennipes with pollinia attached to its thorax. He also noted that his son William Erasmus Darwin saw a fly remove pollinia of O. maculata (a synonym of Dactylorhiza maculata, the heath spotted orchid) in Southampton. In the same note CD recorded having received three flowers of O. latifolia (a synonym of Dactylorhiza incarnata subsp. incarnata, the early marsh-orchid) with a black fly in the nectary from a doctor in Southampton, evidently a reference to Bullar, who practised there (Medical directory 1862).