Pierre François Marie Auguste Dejean

Pierre François Marie Auguste Dejean (; 10 August 1780 – 17 March 1845), was a French soldier and entomologist. Dejean described a large number of beetles in a series of catalogues.

Origins and early career

Dejean was born in Amiens on 10 August 1780, the only child of Jean François Aimé Dejean then a captain in the engineers, and his first wife Alexandrine-Marie-Elisabeth Le Boucher d’Ailly. One summer they were joined in this endeavour by Philogène Auguste Joseph Duponchel, and the three became lifelong friends. In March 1795, with the War of the First Coalition raging, he followed his father into a military career.

Dejean's father was, at that point, Inspector General of Fortifications for the Army of Sambre and Meuse and took on his 14-year-old son as an unofficial aide-de-camp. A commission as a second lieutenant in the infantry came on 5 August 1796, and as lieutenant a year later. Throughout this period he continued to work as his father's aide as the latter took command of the Army of the North. It was during his time in the Army of the North that he abandoned the collection of butterflies, turning to the study of beetles that would become the main passion of his life.

September 1797 saw a reversal in Dejean's fortunes as his father was ousted from command over his refusal to back the Coup of 18 Fructidor. He managed to retain postings in the 8th Demi-brigade and then the 28th Line until his father once again came into favour with the establishment of the Consulate and became a Councillor of State. Called from his regiment to once again become his father's aide, he did so in Italy following the Marengo campaign and back in Paris when he became Minister for the Administration of War. Finally, he transferred to the cavalry becoming a captain in the 20th Dragoons on 3 October 1803.

Napoleonic Wars

At the start of the War of the Third Coalition, Dejean was a newly-promoted chef d'escadron in the 3rd Dragoons and part of the Grande Armée marching against Austria. He fought at Schöngrabern and at Austerlitz. He continued in the war against Prussia and Russia the following year, fighting at Jena, Prenzlau and Lübeck. In Poland, he fought at Pułtusk and took part in Murat's great charge at the battle of Eylau. On 13 February 1807, he was promoted to colonel of the 11th dragoons, replacing a man killed at Eylau. In this role he served with distinction as part of Grouchy's cavalry force at Friedland. and later granted a 10,000 franc endowment from the department of Trasimene.

On 1 June 1808, Dejean was made a Baron of the Empire. That year his regiment joined the Peninsular War in Spain, initially as part of Kellermann's division, and spent two years in the cavalry reserve at Valladolid including fighting at the battle of Alba de Tormes. In 1810, he was part of Masséna's invasion of Portugal, fighting at Bussaco and Fuentes de Oñoro. On 6 August 1811 he was promoted to general de brigade. He funded expeditions to places including Colombia and Mauritius,

In 1821, Dejean began work with Pierre André Latreille on l’Histoire naturelle et iconographique des Coléoptères d’Europe, intended to describe and illustrate every species of beetle in Europe. This massive undertaking was abandoned after three years had passed and three installments had been published.

The July Revolution in 1830 brought about a rehabilitation of Dejean's military career. He commanded a cavalry division in the army sent to support the Belgian Revolution, and served at the siege of Antwerp in 1832. This was his last service under enemy fire, but for the rest of his life he would hold posts as commandant or inspector general of cavalry in one military region or another. His name appears on the south pillar of the Arc de Triomphe.

Family

Dejean married Adèle Barthélemy (d. 1872) on 17 July 1802, the couple had five children:

Adèle Jeanne (1803–1860), married M. Ardènc (1804–1885), Prefect, Director of Police, Councillor of State, Deputy for Aude Pierre Charles (1807–1872) General, Councillor of State, interim Minister for War Dieudonné Marie Louis (1809–1881), baron Dejean, lieutenant-colonel Stéphanie Emma Élisabeth (1815–1878), married Jacques-Alphonse Mahul

Works

Catalogue des Coléoptères de la collection d'Auguste Dejean (1802) Catalogue de la collection de Coléoptères de M. le Baron Dejean (1821) Catalogue des Coléoptères de la collection de M. le Comte Dejean (1833–1836) Catalogue des Coléoptères de la collection de M. le Comte Dejean. Troisième édition, revue, corrigée et augmentée. (1836–1837) with Pierre André Latreille Histoire naturelle et iconographie des insectes coléoptères d'Europe Paris : Crevot, 1822. digitised at Gallica. Spécies Général des Coléoptères, de la collection de M. le Comte Dejean (1825–1838)