How Wood Frogs Survive Being Frozen

Wood frogs survive freezing through a sophisticated biochemical strategy that prevents fatal ice damage to their cells. They don't just tolerate freezing; they manage it with precise control.

The Core Strategy: Controlled Freezing and Antifreeze

The wood frog's secret is controlling where and how it freezes.

Step 1: Sensing the First Ice Crystals

As temperatures drop, the frog's body senses the change. The first ice crystals on its skin trigger a massive physiological response.

Step 2: Flooding the System with "Antifreeze" (Glucose)

The frog's liver rapidly converts glycogen into massive amounts of glucose, which is released into the bloodstream. This glucose acts as a cryoprotectant, lowering the freezing point inside the cells and preventing deadly internal ice formation.

Step 3: Strategic Dehydration

The frog allows water in its blood and extracellular spaces to freeze. This draws water out of the cells through osmosis. The result is a dehydrated, sugar-packed cell that is highly resistant to internal ice crystals.

Step 4: The Frozen State

The frog becomes frozen solid. Its heart stops, blood flow ceases, and all brain activity halts. Up to 70% of its body water turns to ice.

Step 5: The Thaw - A Controlled Reboot

When temperatures rise, the frog thaws from the inside out. The heart is the first organ to restart, often with an erratic beat before returning to normal. Within hours, the frog is fully functional again.

Summary of Key Adaptations

Glucose Production: Floods cells with sugar to lower their freezing point.

Controlled Dehydration: Pulls water out of cells to prevent internal ice damage.

Ice Nucleating Agents: Proteins that ensure freezing starts safely outside the cells.

Specialized Cell Membranes: Flexible membranes that withstand the stress of freezing and thawing.