Although he was neither the first to introduce their farming in the area nor to release them into the wild, he was a major proponent of the animals' introduction and an avid self-promoter, making him a local legend inextricably linked with the origin of nutria in the state.

In 1897 he undertook an Arctic expedition to Point Barrow, Alaska,[2] where he leased an old government refuge station, then owned by the Pacific Steam Whaling Company.

[4][5] He provided cotton, originally intended for taxidermic purposes, for the men's bedding and he hunted wildlife to feed the stranded crew.

[7] At that time Edward took over the family business, E. McIlhenny's Son, which produced Tabasco Sauce, the hot-pepper seasoning invented by his father some 30 years previously.

The nutria introduction began in collaboration with Armand P. Daspit, director of the Louisiana Department of Conservation's Fur and Wild Life Division who approached McIlhenny after reading a bulletin on them from Buenos Aires.

[13] In 1941, he wrote on the potential extinction of the ivory-billed woodpecker, noting its presence in his estate on Avery Island and suggesting that the destruction of old growth forests was key to its demise.

[15] McIlhenny used his 170-acre (0.69 km2) personal estate, known as Jungle Gardens, to propagate both Louisiana-native and imported plant varieties, including azaleas, irises, camellias, papyrus, and bamboo.

[16][17] He wrote numerous academic articles, mainly about birds and reptiles,[18] oversaw the publication in English of two European botanical treatises, and edited Charles L. Jordan's unfinished manuscript The Wild Turkey and Its Hunting (a book often mistakenly attributed to McIlhenny).

McIlhenny's illustrated and written documentation of plant and animal life on Avery Island was donated as a collection to Louisiana State University.