For all known life forms, activity is punctuated by periods of rest. Sleep may be the most familiar, but many other distinct dormant states occur on longer timescales, from weeks to months on end. Such suspended animation has garnered many different names: hibernation and torpor (in mammals and birds), brumation (in reptiles), diapause and quiescence (in insects and nematodes), aestivation (summer dormancy in vertebrates and invertebrates), hypobiosis, cryptobiosis, and latent life (in microorganisms).
This abundance of terms is a consequence of the historically siloed nature of dormancy research — the phenomenon has been noted and described independently in different organisms across centuries. The most well-known of these, however, is likely hibernation. Not only is it an endearing behavioral trait belonging to charismatic fauna like bears and groundhogs, but it is also relatively easy to observe in nature. Where a brumating lizard might not attract much notice, a disheveled bear stumbling out of a den certainly does. And even if it seems far-fetched, the mechanisms behind mammalian hibernation are of increasing scientific interest due to their potential in human life extension and space travel.
While hibernation commands the most attention, a growing body of research suggests that all forms of dormancy reflect similar underlying physiological, metabolic, and gene regulatory mechanisms. Indeed, the dormancy observed in non-mammalian species is no less gripping and ecologically consequential than mammalian hibernation.
In no other group of organisms does the sheer scale of programmed dormancy stand out as staggeringly as in insect diapause. Unlike most other kinds of dormancy, largely characterized by physiological and behavioral suppression, insect diapause is a state of programmed developmental arrest. It’s a pause button pressed on one of the stages of their life cycle — either as eggs, larvae, pupae, or adults, depending on the species.
As such, diapause removes a tremendous portion of insect biomass from active life for large chunks of each year — up to 9 months in some species. At any time, there are an estimated 10 quintillion (1019) individual insects alive, collectively weighing about 1 billion metric tons. Depending on the season and locale, a significant percentage of this biomass can be locked in a dormant state — higher in temperate latitudes, lower in the tropics.
It follows that knowledge of the timing and mechanisms of diapause has massive economic and ecological consequences in agriculture, forestry, vector-borne disease spread, and more.
Diapause Hijacks Developmental Checkpoints
The capacity for dormancy has emerged multiple times throughout biological history. Ancestral microscopic life forms in the ocean experienced boom-and-bust cycles in nutrient availability and other planetary cataclysms. In response, like the Trisolarans from Cixin Liu’s The Three-Body Problem, they developed reversible suppression of metabolism as a bet-hedging strategy to survive Earth’s own “Chaotic Eras.”
When life forms emerged from the oceans and started colonizing the land, they had to reckon with seasonality that is much more starkly pronounced in terrestrial than in marine habitats. This was not merely reactive — multiple taxa like plants, insects, molluscs, and vertebrates harnessed the predictability of seasonal changes to develop an anticipatory response, using photoperiod (duration of daylight), temperature, and other cues as an advanced warning. These dormant states served as “time capsules,” buffering them against complete population collapse in a changing environment.
Dormancy in insects was seen as analogous to mammalian hibernation and was described well before the term “diapause” was introduced into entomologists’ vocabulary. As early as 1734, the French naturalist René Antoine Ferchault de Réaumur published a study on bee physiology and behavior in winter. He wrote:
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