Carl Wilhelm Hahn (lat. Carolus Guilielmus Hahn) (16 December 1786 – 7 November 1835) was a German zoologist and author of the first German monograph on spiders. C. W. Hahn was an all-round natural scientist – not at all unusual for his time. Surprisingly he seems to have been almost forgotten. Even the few biographical dates    , which have been published in secondary literature are not always correct as clarified by P. Sacher in his "attempt at a Biography"  :
Life and lifework
Carl Wilhelm Christian Hahn was born in Weingartsgreuth, Upper Franconia as the first son of Johann Michael Hahn (1734–1824), who was court and palace gardener on the estate of Baron von Seckendorff, later palace gardener for Count Friedrich von Pückler. C. W. Hahn obeyed the general call to arms as early as 1813. He served as a quarter master and in 1816 received his honourable discharge  . Afterwards he lived with his parents in Fürth and, according to Hahn, made up his mind to devote his life to his predilection for natural history, an interest he had had since early childhood and which intensified during his studies in Erlangen. He commenced work on his first ornithological work "Birds from Asia, Africa, America and New Holland". When his "often promised and well earned position"  failed to materialize, Hahn undertook what was for that time, in his field, a very unusual step and went freelance. From then on he called himself a natural historian and occasionally also a scholar. On 24 February 1820, having in the meantime qualified as a Dr. Phil. at the University of Erlangen, he married Victoria Francisca Kaltdorff, née Schaefer. His wife, the widow of a doctor of medicine, was about five years older than he, and had three children by her previous marriage. She was at this time without means, but was expecting quite large inheritance from her maternal uncle before long. Their own child Anna Friedericke was born at the end of 1820 or 1821.
It can be assumed, that Hahn was in close contact with the universally known natural scientist Jakob Sturm and probably with his two sons. He named a spider species after Jakob: Araneus Sturmii, now Atea sturmi (Hahn, 1831)  . His relationship with Johann Georg Wagler must have been similarly close. He also named a spider species after him: Lÿcosa Waglerii, now Pardosa wagleri (Hahn, 1822)  . Nothing reliable is known about other contacts within the remarkably productive Nuremberg zoologist scene. Nor is there any proof, that Hahn knew Franz von Paula (von) Schrank personally, a highly regarded natural scientist, to whom he dedicated the "Monograph on Spiders". The scientific value of Hahn's lifework in natural history varies. His ornithological work, for example, never had any discernible influence on this field. On the other hand, Hahn's work on the true bugs (Heteroptera) is just as important as his works on spiders (Araneae). One species of bug even carries his name: Lopus hahni Stål, 1860. He was also given this honour in the field of arachnology: Carl Ludwig Koch, who continued "Die Arachniden" after Hahn's death, called a genus after him in 1841 (Hahnia), on which later the name of the whole family was based – Hahniidae Bertkau, 1878.
According to L. Gebhardt  Hahn died in Nuremberg on 7 November 1835, "of a lung complaint in the prime of life".
About the rarity of the work: today only about 14 – partially incomplete – copies are known. They were recorded and examined by Sacher  from Germany (Wittenberg, Berlin, Jena, Darmstadt, Erlangen, Kiel, Munich, Frankfurt/M.), England (London), U.S.A. (Cambridge/Mass.), Austria (Vienna) and France (Paris). "Monographie der Spinnen" has become a rarity already at the beginning of the 20th century.  This rarity can be explained by the fact that only small editions were produced: "More than a hundred copies of each installment will not be produced", remarked Hahn on this subject in 1820. The great rarity of complete copies probably results primarily from the long gap between installments. It has not been possible to ascertain whether Hahn broke with his publisher or Lechner with him. However, a separation took place some time before the publication of the sixth installment. Indeed, in 1831 the first installment of "Die Arachniden" had already appeared in Zeh's Bookshop in Nuremberg as an obvious substitute for the "Monographie der Spinnen". It was more accessible and thus also better known than the "Monographie der Spinnen". In the sixth installment of the "Monographie der Spinnen" the publisher Lechner 1831 inserted a small format "message", which announced that Hahn had been relieved as editor. Probably the contents of the sixth installment still can be wholly attributed to Hahn, even though he had only admitted to the first five installments. For obvious reasons the publisher Lechner was not in a position to print anything new, even though he still had original drawings in his possession, which he published without Hahn's consent. For this reason alone it was already impossible to compete with Hahn's new project. It was therefore not surprising that the promised ninth installment failed to appear.
In the past there has been some confusion regarding the year of publication, particularly of the installments 2, 5 and 7.       Probably this confusion has been caused both by the partial absence of dated forewords and of dust jackets for the individual installments, as by the fact, that the bookshop and later (1822) publisher Lechner did not only provide installments which were sold later with a non-original cover, but in a good many cases also overwrote the year of publication with the year of sale. On basis of recent investigation  the correlation between installments and the years of publication has been clarified as follows:
A definitive representative copy of "Monographie der Spinnen" probably does not exist (any more). The available copies differ in several features as detailed pointed out by Sacher  . For this reason it was used a combined version for the reprint of 1988.
But "Monographie der Spinnen" is far more than just a bibliophilic work.
Firstly it includes nine still valid first descriptions of spider species. In the 19th century it was not unusual, that a majority of "new species" had been previously described by other authors. This is because in contrast to the modern differentiation of species, the genital structures were not taken into consideration at that time. For that reason smaller differences in the colourings and markings have possibly given rise to different species designations. At any rate a sixth of the forms described by Hahn are still valid today. That Hahn was a good observer and gave exact descriptions is shown clearly by the example of Eresus annulatus (= E. sandaliatus (Martini & Goeze, 1778)) and E. cinnaberinus (= E. kollari Rossi, 1846). After more than 150 years arachnologists follow his separation of these taxa today again.    
Secondly its monographic character is remarkable. It is the first monographic work for spiders in German language. Further 180 years ago it was very unusual to use a group like spiders as a sole subject of a book. Apart from a natural history of spiders by the Frenchman Walckenaer in 1806  there had been no work of that time which exclusively had spiders as its subject.
Thirdly spider illustrations in the "Monographie der Spinnen" show Hahn to be an above average artist and lithographer.
Finally "Monographie der Spinnen" and "Die Arachniden" are different ways of carrying out the same project and they can both be considered as autonomous works, whereas Brignoli  – an important cataloguer in arachnology – regarded "Monographie der Spinnen" only as a sort of blueprint for "Die Arachniden".
Until the end of the 18th century all studies of spiders, scorpions and related forms were treated as part of the wider study of entomology, for these were described as wingless insects and included in one genus, the Aranea of Linnaeus, of perhaps 500 different species. Based on Walckenaer's "Fauna Parisienne" (1802) Latreille established the first set of genera for spiders in his work, which is marking the real beginning of arachnological systematics, and which was extended by Walckenaer into the important "Histoire naturelle des Insectes Aptères" (1837–1847). During the mid-19th century the centre of activity shifted away from France to Germany. An important part of this shift was due to the 14-volume work of C. W. Hahn and C. L. Koch "Die Arachniden" (1831–1848). In contrast to the French manuscripts with their terse descriptions and infrequent illustrations, the two-thousand-plus pages of beautiful coloured plates of this work captured the attention of zoologists everywhere. The French arachnologist Simon was incited by the high number of species, described from Germany in "Die Arachniden", while from his native France almost nothing had been done. In particular "Die Arachniden" was very influential in founding a German tradition of active interest in arachnology which flourished for nearly a century. Its major shortcoming, as was realized later, was the lack of a natural scheme of classification, particularly above the family level.  
(all illustrated by Hahn himself)
- Voegel(,) aus Asien, Africa, America, und Neuholland, in Abbildungen nach der Natur mit Beschreibungen. 19 installments, Lechner: Nuremberg, 1818–1836.
- Monographia Aranearum – Monographie der Spinnen. 8 installments, Lechner: Nuremberg, 1820–1836.
- Naturgetreue Abbildungen zur allgemeinnützigen Naturgeschichte der Thiere Bayerns. Author: Nuremberg, 1826–1828.
- Icones ad monographium Cimicum Nurnberg, Lechner,1826.
- (together with Jacob Ernst von Reider Fauna Boica, oder gemeinnützige Naturgeschichte der Thiere Bayerns. Zeh: Nuremberg, 1830–1835.
- Die Arachniden. Getreu nach der Natur abgebildet und beschrieben. 2 volumes, Zeh: Nuremberg, 1831–1834 (from the 3rd volume onwards continued by C. L. Koch).
- Die wanzenartigen Insecten. Getreu nach der Natur abgebildet und beschrieben. 3 volumes, Zeh: Nuremberg, 1831–1835 (from the 4th volume onwards continued by G. A. W. Herrich-Schäffer).
- Gründliche Anweisung Krustenthiere, Vielfüße, Asseln, Arachniden und Insecten aller Klassen zu sammeln, zu präpariren, aufzubewahren und zu versenden. Zeh: Nuremberg, 1834.
- Ornithologischer Atlas oder naturgetreue Abbildung und Beschreibung der aussereuropäischen Vögel. 6 installments, Zeh: Nuremberg 1834–1836 (continued by H. C. Küster).
- Icones Orthopterorum. Abbildungen der hautflügeligen Insecten. 1 installment, Lechner: Nuremberg, 1835.
About C. W. Hahn
- "This person is indeed extremely foolish, but is incidentally polite, draws exceedingly well, has a beautiful hand, has much knowledge of natural history and botany, and is skilled in stuffing birds. However, because of his foolishness he requires strict supervision. His other talents and capabilities make him worthy of some consideration.", Count Pückler in 1805 to colonel of the infantry regiment, Erbach von Henneberg.