Insects living in the temperate climate include summer diapause, or aestivation, in their seasonal cycle to solve various problems related to adaptation to unfavorable seasons. Unlike winter diapause, summer diapause occurs in summer and is usually terminated in autumn when active feeding, development, and/or reproduction are restored. Typically, high temperature and long day induce summer diapause and then maintain it, whereas short day and low temperature prevent induction of this diapause or terminate it. The summer diapause syndrome is basically similar to that of winter diapause; it includes prior development of large fat body, decreased level of metabolism, increased general resistance to unfavorable abiotic and biotic conditions, etc. Inhibition of morphogenesis and gametogenesis is under the control of the endocrine system. The onset of summer diapause is often accompanied by migrations to varying, sometimes significant distances to the sites of aestivation. The selective factors responsible for evolution of summer diapause vary between insect species. Climatic factors and, consequently, availability and abundance of food, as well as pressure of predators and parasites are likely to be the main factors that stimulate its occurrence. In some species, prolonged diapause begins in spring or early summer and ceases only after over-wintering. When studied in detail, such prolonged diapause often turns out to be a sequence of two independent diapauses, summer and winter ones, occurring in succession without detectable external changes.