Are the plummeting temperatures leaving you chilled to the core? Wishing the deep freeze is over soon? While we can get warm and cozy staying indoors with heating and can throw on layers of clothes to cover up our body when out in the bitter cold, what about insects? Ever wondered how they cope with the long, harsh winter in the Arctic?
Insect larvae have evolved their own nifty survival strategies: they either tolerate the formation of ice crystals in their bodies during freezing or avoid freezing altogether. One method of avoiding freezing is through a phenomenon known as supercooling where the freezing point of the body fluid is lowered so that it remains liquid even below its normal freezing point. How is this achieved? Some bugs produce antifreeze proteins or chemicals such as glycerol that inhibit ice crystal formation upon contact with external ice – much like the antifreeze in your car. Glycerol interferes with the hydrogen bonding between water molecules, preventing them from bonding with each other, thereby disrupting the formation of ice crystals.
The lowest recorded deep supercooling temperature for an Alaskan red flat bark beetle larvae, Cucujus clavipes puniceus, was -58°C (-72.4°F). But Sformo and colleagues noticed that some larvae managed to avoid freezing even as low as -80°C (-112°F), which is not possible solely by antifreeze. They suspected that they turned into glass so they decided to investigate how and reported their findings in a 2010 paper in the Journal of Experimental Biology.
During fall, they collected larvae from under dead tree barks at two sites, Fairbanks and Wiseman, both of which are located in the interior of Alaska where the official minimum temperatures have plunged as low as -50°C (-58°F). After leaving the larvae out on the ground in a plastic container for 1 to 4 months to acclimatize, they shipped them to the lab where they cooled them and measured the supercooling points, water and glycerol content, and change in heat capacity.
They found that over half of the larvae collected from both sites did not freeze between -60°C and -70°C (-76°F and -94°F). Instead, the water in their bodies transformed into a non-crystalline glass-like state – a process known as vitrification. A few larvae were tough enough to withstand exposure down to -100°C (-148°F) and astonishingly remained unfrozen even at an unimaginable -150°C (-238°F) – a temperature that would easily wipe out much of life on Earth.
The larvae achieved this impressive feat by dehydrating themselves so less water is available to freeze and with lower water content the concentration of antifreeze proteins rises as much as five-fold. Glycerol becomes highly concentrated, which causes body fluids to transition into a viscous glass at temperatures below -58°C (-72.4°F).
The researchers suggest that as fall approaches, the larvae start producing antifreeze proteins that can supercool them to -20°C (-4°F). Towards winter they start to dehydrate, causing accumulation of glycerol and concentrating the antifreeze proteins that can protect down to -40°C (-40°F). As it gets colder, they desiccate even further, increasing their glycerol concentration substantially, which promotes vitrification that can shield them from brutally cold temperatures.
Vitrification can protect the larvae from damage especially when there is low snow cover to insulate them, which was the case in Wiseman during 2006 and 2007.
Sformo’s team will test whether these amazing creatures can actually spring back to life after vitrification in the lab.
Sformo et al. (2010). Deep supercooling, vitrification and limited survival to –100°C in the Alaskan beetle Cucujus clavipes puniceus (Coleoptera: Cucujidae) larvae. The Journal of Experimental Biology, 213, 502-509. DOI: 10.1242/jeb.035758.