After leaving school, Haldeman took over management of his father's new sawmill and became a silent partner with two of his brothers who started an iron manufacturing business in the area. He eventually became an authority on smelting iron. However, he was always drawn to science and often neglected the family businesses in pursuit of these interests. The monograph was well received by the scientific community in America and Europe. In an addendum he described
Scolithus linearis, a
trace fossil of some burrowing organism, the most ancient organic remains known at the time. In 1844 he wrote a paper, "Enumeration of the Recent Freshwater Mollusca Which are Common to North America and Europe", where he laid out in detail the case for
Lamarckian evolution and
transmutation of species. In 1861,
Charles Darwin wrote in a preface to his
On the Origin of Species an acknowledgment of Haldeman's ideas in support of evolution. He was elected as a member to the
American Philosophical Society in 1844. In 1842, he was instrumental in the establishment of the Entomological Society of Pennsylvania, the first scientific society formed to study insects in America. Haldeman's participation in the society put him in regular contact with other leading American entomologists including
Frederick E. Melsheimer and
John G. Morris. His first entomological paper was the "Catalogue of the Carabideous Coleoptera of South Eastern Pennsylvania," published in 1842. Over the next 15 years he published many papers on the systematics of beetles and other insects, describing many new species. His ear was remarkably sensitive, and he discovered a new organ of sound in lepidopterous insects, which was described by him in
Benjamin Silliman's
American Journal of Science in 1848. In 1852 he wrote a description of the insects collected by the
Stansbury survey of the Great Salt Lake. In the 1850s, Haldeman's focus turned to the study of language. He carried out extensive research among
Amerindian dialects, and also in
Pennsylvania Dutch, besides investigations in the English, Chinese, and other languages. Haldeman was an earnest advocate of spelling reform. He was a member of many scientific societies, was the founder and
president of the American Philological Association, and one of the early members of the
National Academy of Sciences. In 1858, Haldeman was awarded the Trevelyan Prize, given by the Phonetic Society of Great Britain, for his article entitled "Analytic Orthography". ==Works==