Climate change affects insect populations in various ways, such as north- or southward range expansion, changes in the number of annual generations, and asynchrony between the emergence season of insects and host plant phenology. We often try to simply attribute drastic changes in insect population density to global warming. However, causality does not seem to be that simple. Long-term field surveys are essential to explain causal relation between drastic changes and global warming. How will be insect life affected by global warming?