Teacher and botanist who spent several years in Noumea, New Caledonia. Le Rat shared his passion for natural history with his father, a gardener, and his wife, with whom he lived in Alençon in France. Filled with a desire to explore the natural history of far away lands, Le Rat obtained a position as a teacher in Noumea in 1900. In his spare time he made numerous excursions to collect plants, shells and minerals, however he was limited to the environs of Noumea without a government permit to explore the interior (which he later obtained).

In 1902 Le Rat met the botanist Rudolf Schlechter, whom he accompanied on several collecting trips. He was thereafter commissioned to collect plants for the Jardin Colonial at Nogent-sur-Marne, Paris, and in 1906-1907 made two fruitful trips to the mountain chain in the centre of New Caledonia, accompanied by his wife. By 1910 they had visited most parts of the main island and had collected more than 5,000 phanerogams plus thousands of cryptogams, mosses and fungi, in addition to molluscs, crustaceans, insects, birds and minerals.

Recognised for his work in New Caledonia, Le Rat was named a correspondent of the Paris Museum of Natural History and returned to France for a well-earned rest in June 1910, apparently full of health and with plans for further exploration. The plans were never to be realised, however, for he died, only in his late thirties, in October that year. Duplicates of Le Rat's specimens were distributed by E.G. Paris, who published his mosses in 1909. Stephani and G. Brotherus also determined some of his specimens.

Sources:
A. Berteau, 1911, "Nécrologie. August-Joseph Le Rat", L'agriculture pratique des pays chauds, 11: 423
L. Letacq, 1912, "Auguste Le Rat", Bullétin de la société historique et archéologique de l'Orne, 31(1): 463-469
G. Sayre, 1975, "Cryptogamae Exsiccatae: an annotated bibliography of exsiccatae of algae, lichens, hepaticae, and musci. V. Unpublished Exsiccatae: I. Collectors", Memoirs of the New York Botanical Garden, 19(3): 359.