Robert McLachlan (or M’Lachlan or Mac Lachlan) was an English entomologist.
McLachlan was born on 10 April 1837 in Ongar, Essex. He was the son of Hugh McLachlan. He was educated in Ilford and inherited sufficient money to enable him to devote himself enitirely to the study of natural history and to travel. He devoted himself initially to botany before specializing in the study of the Neuroptera.
McLachlan was the first editor of the review Entomologists' Monthly Magazine. He became a member of the Entomological Society of London in 1858, its secretary in 1868 to 1872, treasurer from 1873 to 1875 and from 1891 to 1904 and president 1885 to 1886. He was also a member of the Linnean Society of London from 1862, of the Royal Society from 1877, the Zoological Society of London from 1881 and of the Royal Horticultural Society from 1888. He was also a member of the council of the Ray Society and a member of various British and foreign learned societies. He died on 23 May 1904 in Lewisham, close to London.
Among his publications are