Biological Antifreeze in Plants & Animals

The darkling beetle (Upis ceramboides) lives beneath peeling birch bark throughout Southcentral and Interior Alaska, surviving temperatures as low as -76°F (-60°C)!

Unlike many insects that use simple glycerol, the Upis beetle produces non-protein xylomannan—a specialized sugar-lipid molecule that anchors to ice crystal faces, preventing them from growing.

Pure distilled water freezes at exactly 32.0°F (0.0°C). However, when solutes (sugars, salts, alcohols, or proteins) dissolve in water, they disrupt the formation of hydrogen-bonded ice lattices.

In this classroom lab, students measure the freezing point of pure water vs 10% sugar solution vs 20% salt brine using crushed ice and rock salt baths.

Deciduous trees (birch, aspen) drop their broad leaves before winter to prevent desiccation. But spruce trees keep their needles all year!

In autumn, spruce needles pump water out of cells into intercellular spaces, concentrating sugars and resins inside. The remaining intracellular fluid supercools down to -40°F without forming a single ice crystal.

Cold-hardened insects and plants require steady, uninterrupted cold. When mid-winter warm spells push temperatures to 45°F, organisms de-harden and metabolize their antifreeze sugars prematurely.

When freezing temperatures suddenly return 48 hours later, unprotected tissues freeze and suffer catastrophic winter kill.

Students graph their classroom freezing point depression data and compare calculated freezing curves.

We reflect on how protecting old-growth spruce canopies provides crucial thermal buffers for overwintering wildlife.