stylistic:tone
Tolerance of extreme environments

About 90% of beetle species enter a period of adult diapause, a quiet phase with reduced metabolism to tide unfavourable environmental conditions. Adult diapause is the most common form of diapause in Coleoptera. To endure the period without food (often lasting many months) adults prepare by accumulating reserves of lipids, glycogen, proteins and other substances needed for resistance to future hazardous changes of environmental conditions. This diapause is induced by signals heralding the arrival of the unfavourable season; usually the cue is photoperiodic. Short (decreasing) day length serves as a signal of approaching winter and induces winter diapause (hibernation). A study of hibernation in the Arctic beetle Pterostichus brevicornis showed that the body fat levels of adults were highest in autumn with the alimentary canal filled with food, but empty by the end of January. This loss of body fat was a gradual process, occurring in combination with dehydration.

All insects are poikilothermic, so the ability of a few beetles to live in extreme environments depends on their resilience to unusually high or low temperatures. The bark beetle Pityogenes chalcographus can survive −39 °C whilst overwintering beneath tree bark; the Alaskan beetle Cucujus clavipes puniceus is able to withstand −58 °C; its larvae may survive −100 °C. At these low temperatures, the formation of ice crystals in internal fluids is the biggest threat to survival to beetles, but this is prevented through the production of antifreeze proteins that stop water molecules from grouping together. The low temperatures experienced by Cucujus clavipes can be survived through their deliberate dehydration in conjunction with the antifreeze proteins. This concentrates the antifreezes several fold. The hemolymph of the mealworm beetle Tenebrio molitor contains several antifreeze proteins. The Alaskan beetle Upis ceramboides can survive −60 °C: its cryoprotectants are xylomannan, a molecule consisting of a sugar bound to a fatty acid, and the sugar-alcohol, threitol.

Conversely, desert dwelling beetles are adapted to tolerate high temperatures. For example, the Tenebrionid beetle Onymacris rugatipennis can withstand 50 °C. Tiger beetles in hot, sandy areas are often whitish (for example, Habroscelimorpha dorsalis), to reflect more heat than a darker color would. These beetles also exhibits behavioural adaptions to tolerate the heat: they are able to stand erect on their tarsi to hold their bodies away from the hot ground, seek shade, and turn to face the sun so that only the front parts of their heads are directly exposed.

The fogstand beetle of the Namib Desert, Stenocara gracilipes, is able to collect water from fog, as its elytra have a textured surface combining hydrophilic (water-loving) bumps and waxy, hydrophobic troughs. The beetle faces the early morning breeze, holding up its abdomen; droplets condense on the elytra and run along ridges towards their mouthparts. Similar adaptations are found in several other Namib desert beetles such as Onymacris unguicularis.

Some terrestrial beetles that exploit shoreline and floodplain habitats have physiological adaptations for surviving floods. In the event of flooding, adult beetles may be mobile enough to move away from flooding, but larvae and pupa often cannot. Adults of Cicindela togata are unable to survive immersion in water, but larvae are able to survive a prolonged period, up to 6 days, of anoxia during floods. Anoxia tolerance in the larvae may have been sustained by switching to anaerobic metabolic pathways or by reducing metabolic rate. Anoxia tolerance in the adult carabid beetle Pelophilia borealis was tested in laboratory conditions and it was found that they could survive a continuous period of up to 127 days in an atmosphere of 99.9% nitrogen at 0 °C.