Islands are hotspots of biodiversity and extinction. It is critical to study their unique island life before it is lost forever. The Desventuradas Islands, comprised of San Felix and San Ambrosio islands, are a volcanic archipelago 850 km off the coast of Chile. They are key to understanding the diversification processes which shaped the flora and fauna of other Chilean oceanic islands such as the Juan Fernandez Archipelago. But, the biogeographic affinities between these archipelagos are still poorly known. Over the last century, the plant and animal communities present in the Desventuradas have radically changed due to invasive mammal introductions. Here, focusing on terrestrial invertebrates, we: (1) confirm the presence of described endemic species, (2) detect new species records and (3) assess the biogeographic affinities between the Juan Fernandez and Desventuradas archipelagos. In September 2018, San Ambrosio was surveyed using different methods (hand collecting, beating sheet, entomological net, pitfall traps and light traps) at night and during the day. A total of 35 morphospecies were collected. Four endemic species were found, in addition to several previously described higher taxonomic groups with undescribed species. Collecting methods were not successful in detecting another nine previously described endemic species. There was a total of 28 new records, including a new land snail, a new Isopoda and representatives of five spider families. Twelve of all the recorded genera from Desventuradas Islands have known relatives in the Juan Fernandez Archipelago. Five of them were not previously known for San Ambrosio, reinforcing the biogeographic affinities between both archipelagos. This research highlights the urgency of surveying islands subject to a multitude of threats, including climate change and invasive species, to generate baseline data and place the island's fauna in a broader biogeographical context.