The Drosophila subobscura larvae were found to be unable to form a capsule around a parasitic egg or an inert foreign body. The specificity and physiological causes of this incapacity were also explored: analysis of the circulating hemocytes showed that no lamellocyte was ever found in D. subobscura host larvae. Therefore, the fly D. subobscura is the first discovered animal species to present an innate immunodeficiency against a wide range of parasites. This is contrary to the theories that propose that all organisms, in natural conditions, are potentially able to defend themselves against parasitization. This unexpected finding opens evolutionary debates about the cost of immune resistance not only at the level of a population, but also of a whole species. We believe this species of fruitfly could become a new model system to study genes involved in hematopoïesis, and in a larger context to better understand defence reactions in organisms.