In the Ethiopian mountain area of Wag Hamra, the use and knowledge of household plant-based remedies to treat specific crop, livestock and human insect pests represent a large, diversified and complex field of ethnobotany that hints at the antiquity of human presence in the area. From a synchronic perspective, this complexity stems from the intermeshing, within the broader context of pest management, of clear ethnoentomological and ethnobotanical patterns, of which the Orthodox Christian religion, processes of acculturation between the original Agaw people and their Amhara neighbours, gender, altitude and cultural perceptions of altitude are key dimensions. The extreme ruggedness of the landscape, the resulting fluctuations in plant distribution and the very "localised" nature of the ethnobotanical knowledge of farmers converge to raise intracultural variability to very high levels. Current patterns and mechanisms of knowledge transmission, particularly among children, suggest that intracultural consensus on botanical pest management is at its highest at the level of microwatersheds not exceeding 20 km2. Multipurpose plant use is not random but patterned according to continua of plant use that are indicators of long term processes of innovation, change and knowledge differentiation. These continua reflect the high degree of relatedness between the use of plants for pest management and the use of household fumigants, of cosmetics, of remedies for skin problems and of evil eye protections for crops. The introduction in recent decades of soap and chemical pesticides has had a significant impact on the pest management strategy of farmers. For selected pests, these changes have resulted in sharp decreases in plant use, but the overall figures of plant use and knowledge point to the co-existence of synthetic and plant remedy use and to the absence of significant ethnobotanical knowledge losses. However, the simultaneous sharp decline of the plant resources in the area could disturb this fragile equilibrium in the near future.