The ecological characteristics of the typical locality ofAcanthogonatus tacuariensisare given. The species inhabit two types of ecological subformations (= micro‐habitats): spaces between the inferior branches of the shrubs and the soil surface and interface soil surface underside free stones. Therefore, it is a component of the criptozoic fauna of Uruguay that sometimes lives in sites of difficult access to man. It has a characteristic behavioural ecology: the females and the juveniles make waterproof tunnel‐webs within which they stay during the scotophase.