The Himalayan region, renowned for its rich biodiversity and stunning landscapes, harbors a delicate ecosystem where certain insects act as keystone species, exerting a disproportionate influence on the entire system. This chapter explores the significance of keystone insects, particularly ecosystem engineers like ants and termites in the Himalayas, and aquatic insects in stream and river ecosystems. Keystone insects play crucial roles in nutrient cycling, habitat modification, and the regulation of other species, contributing to the resilience of these ecosystems. This review study also addresses the impact of human activities on keystone insects and delves into the effects of climate change, emphasizing the vulnerability of these species to environmental shifts. Additionally, the role of predatory insects in herbivore regulation is discussed, showcasing their importance in maintaining ecological balance. The chapter underscores the need for research and conservation efforts to safeguard keystone insects and preserve the intricate relationships within these ecosystems.