The World Arachnid Catalog was introduced 2021 as an amalgamation of the well-established World Spider Catalog, Mark Harvey’s Catalogue of the Pseudoscorpionida, published in 1991 by Manchester University Press, later provided in an on-line database published by the Western Australian Museum (the last version 3.0 contained published data up to the end of 2011), and the Smaller Arachnid Order catalogs, hosted previously by the Western Australian Museum and last updated in 2013 by Mark Harvey. The World Arachnid Catalog follows more or less the standard of the World Spider Catalog and presents, in addition to spiders, all available taxonomic information for Amblypygi, Pseudoscorpiones, Ricinulei, Palpigradi, Schizomida, Solifugae and Uropygi in a single location and a standardized format.

The small arachnid orders do not seem to contribute much in terms of species, with around 6000 species to the approximately 50,000 spider species (2021). However, in addition to a gain in diversity and a further step towards a complete record of the arachnids, the World Arachnid Catalog also lists the fossil species from the small arachnid orders, so that the former diversity can be estimated in addition to the current diversity.

The World Arachnid Catalog is a curated database, thus, users are invited to add lacking information or to correct mistakes (see the contact details for each catalog). Such comments will be verified by specialists. The World Arachnid Catalog is a joint effort of the scientific community.