Transgenerational (usually maternal) immunity has evolved in vertebrate species but also in some invertebrates. Yet, the ecological factors driving its evolution remain poorly understood. In our study, we develop a theoretical model and predict that longevity and dispersal distance should promote the evolution of transgenerational immunity. Moreover, we show that the experimental studies published to date in invertebrates confirm our theoretical predictions. Indeed, as expected, lifespan and dispersal correlate with the transfer immunity to offspring. We discuss the implications of our work for the study of the evolution of immunity in both invertebrate and vertebrate species.