In this paper I will sketch an Umwelt ethics, i.e., an ethics that rests heavily on fundamental features of Jakob von Uexküll’s Umwelt theory. In the course of an interpretation of the Umwelt theory, a number of concepts are introduced. These include ontological niche, common-Umwelt, total Umwelt and bio-ontological monad. I then present an Uexküllian reading of the deep ecology platform. It is suggested that loss of biodiversity, considered as a physio-phenomenal entity, is the most crucial aspect of the ecological crisis, which can be understood as an ontological crisis.