Rapid expansion of internet connectivity and mobile technology has led to a fundamental transformation of the retail landscape. Sales of undomesticated animals as pets have rapidly expanded beyond ‘brick-and-mortar’ retail stores to include a growing number of internet marketplaces that provide more convenient purchasing and access to trendy, sometimes unique, species. In doing so, the internet has created opportunities for new and long-distance trade routes for live organisms and increased accessibility to new source pools of invasive species. Despite wide recognition of trade in vertebrates, many knowledge gaps exist regarding the online global trade of pet invertebrates. Freshwater crayfish, for example, are very popular pets among aquarium hobbyists, and many species in trade have proven to be particularly invasive, impacting ecosystems, spreading disease, and inflicting significant economic damage. Here, we provide the first global assessment of the online trade in ornamental crayfish. By systematically examining e-commerce marketplaces and peer-to-peer platforms in multiple languages, we: (1) identified freshwater crayfish currently associated with online pet marketplaces; (2) determined the volume, economic value and geographic routes of crayfish pet trade; and (3) evaluated the risk of establishment in the wild of nonnative crayfish species offered on marketplaces. Precise characterization of the online pet trade market is fundamental to support the development of regulations and biosecurity policies to prevent trade in species invasions. This study reveals that the taxonomy, geography and economics of global online crayfish trade is vast and requires greater scrutiny.