Woolly Bear caterpillars live in the Arctic Circle and spend most of the year in a dormant state. When temperatures fall to near zero or sub-zero levels, these caterpillars synthesize glycerol and become dormant. The glycerol is a cryoprotectant that acts as a form of antifreeze in the caterpillar's tissues, allowing it to survive the freezing temperatures.
The caterpillars come out of the dormant state for only one month of the year, in which they feed and prepare for the next dormant session. Because they remain in dormancy for such long periods, these Arctic-dwelling caterpillars have a much longer life-cycle than other caterpillars. Some Woolly Bear caterpillars have survived in the larval stage for over a decade.
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