The Museum’s collections of Arachnida are among the largest of their kind in the world. The term Arachnida covers the following groups: Acari, Amblypygi, Araneae (spiders), Opiliones (harvestmen), Palpigradi, Pseudoscorpiones, Ricinulei, Schizomida, Scorpiones, Solifugae and Thelyphonida.
The specimens in the collection come from all regions of the world, represent strictly tropical groups as well as to those found in temperate areas, such as Europe. They come from a wide range of habitats, including caves, but aquatic forms are only represented by certain mite groups and one species of spider. They are conserved in jars of 75% alcohol, or on microscope slides. All the specimens, whether types or not, are stored in two places: a main reserve in the Museum’s "Zoothèque" (an underground storage facility), and a smaller collection room in one of the research buildings.
Around 26,000 spider species, of which around 12,000 are represented by types, are present at the Museum. This historical collection was started in the nineteenth century by early workers like Lucas, but it only started to become of worldwide importance from the 1860s onwards through the contributions of Eugène Simon (1848‒1924). Simon was an amateur arachnologist who was still only 16 when he wrote his first book, Histoire Naturelle des Araignees, which is still an important reference work. The collection has continued to grow over the years, enriched in particular through the addition of the Bonnet, Denis, Dresco, Legendre and Strand collections. The Scorpion collection is represented by thousands of specimens including over 500 types, and expanded rapidly in the 20th century in particular, due to the work of Max Vachon and, more recently, Wilson Lourenço. Similarly, the Acari collection, comprising 20,000 lots, has particularly important holdings of Trombidioidea and feather mites, thanks to the work of André and Trouessart at the museum. Another group that is particularly well represent is Pseudoscorpions, with 7,000 lots, including many types of species described by Simon, Vachon and Heurtault. Opiliones include 2,000 samples and the remaining groups of Arachnids comprise about 1,500 samples.
These collections have a primarily scientific purpose. New specimens are added each year, thanks to donations of varying sizes, many of which come from recent expeditions. When possible, specimens are identified by specialists at the museum, by visiting researchers or by specialists at other institutes, but the collections also contain an important amount of unidentified material that is stored for future study. The main research activity themes relevant to the collections are taxonomy (description, inventory and naming), phylogeny (the study of kinship between living beings), biodiversity studies and environmental management. The amount of material loaned from these collections is considerable (around a hundred items sent out each year).
Computerisation of the collections began in the 2000s. The museum’s general database currently includes some 3,000 spiders, 700 scorpions and 200 other arachnids (in particular Opiliones and Amblypygi). While many of the systematic files are still stored manually, they can easily be consulted by visitors. A specialist library with historic reference works and more recent offprints is also accessible to arachnologists from outside of the department, under the supervision of the unit’s researchers.