'Multiple causation' is the canon of contemporary epidemiology, and its metaphor and model is the 'web of causation.' First articulated in a 1960 U.S. epidemiology textbook, the 'web' remains a widely accepted but poorly elaborated model, reflecting in part the contemporary stress on epidemiologic methods over epidemiologic theories of disease causation. This essay discusses the origins, features, and problems of the 'web,' including its hidden reliance upon the framework of biomedical individualism to guide the choice of factors incorporated in the 'web.' Posing the question of the whereabouts of the putative 'spider,' the author examines several contemporary approaches to epidemiologic theory, including those which stress biological evolution and adaptation and those which emphasize the social production of disease. To better integrate biologic and social understandings of current and changing population patterns of health and disease, the essay proposes an ecosocial framework for developing epidemiologic theory. Features of this alternative approach are discussed, a preliminary image is offered, and debate is encouraged.