It’s Oct. 20 and you wake up to 40 degrees.

After months of 90s, 80s, and 70s you’re freezing. Well not really. With intellect we’ve constructed abodes with a variety of heat sources and have perfected the manufacture of the best insulating clothing and footwear. So we really don’t “freeze,” but many animals do.

Now move ahead, it’s late February or early March and a sunny, warm day. You look at the ceiling in your kitchen and low and behold there are house flies there.

Where did they come from? Well house flies and green bottle flies, both common around humans, have probably spent the winter tucked under your siding or in crevices in trees. And yes, they survived January’s 5 or 10 degree nights. In fact they survived freezing temperatures for months. Didn’t they freeze to death?

Technically, their body temperatures matched that of their surroundings and as long as they were able to not dry out, they could survive. House flies, as a night of freezing temperatures approaches, quickly produce their own antifreeze (a type of alcohol) that gives them the ability to drop well below freezing and survive.

They aren’t the only animals to do this. On your autumn bike ride, hike or country drive, you see banded woolly bear caterpillars scurrying (at caterpillar speed) in front of you. They have finished feeding for the year and are heading to protected areas to overwinter.

Woolly bear caterpillars have stored glycogen in their bodies but somehow, within hours of freezing, they convert this to two types of alcohol (not beer or vodka) glycerol and sorbitol. Those two alcohols reduced the freezing point of their blood to 17 degrees Fahrenheit. Essentially, they quickly make their own antifreeze. Somehow, when they “know” there are no more freezes in spring, they spin a cocoon to later become an Isabella moth. This insect overwinters as a larva (caterpillar.)

Mourning cloak butterflies handle winter differently. The caterpillars after feeding on willows, pupate, emerge as adults butterflies, then find a hollow tree to remain all winter. They too produce alcohol to serve as antifreeze. They are the first butterflies you’ll see in spring. Tent caterpillars, those with the white “nest” in the forks of cherry trees, overwinter as eggs in a glued mass to a twig. Again, with glycerol as an antifreeze.

What about the more advanced animals? Wood frogs, our earliest amphibians to emerge in spring can freeze. They survive the winter the same as three other common frogs, the spring peepers, gray tree frog and chorus frog. Surprisingly, these amphibians usually bury under leaf litter or in the top layer of soil, under a layer of snow cover, and surprisingly, freeze.

Up to 65 percent of these frogs’ total body water becomes ice. But the individual cells do not freeze. They are frozen, but do not die. However, if somehow their temperature got below 15 degrees, they will succumb.

As I read more about winter survival I am totally amazed at how nature’s creatures and plants have adapted.

I’m sure glad we have found ways to keep warm in the coldest season. Keep warm on your cold, late winter nature hike knowing you may be walking near some “frozen frogs” under some nearby soil or snow cover. Brrrr.

Test Your Outdoor Knowledge: True/False. Bald faced hornets, the ones with the large, gray paper nests, survive all winter in their nests and resume feeding in spring?

Last Week’s Nature Trivia: Bald eagles’ favorite food is indeed fish, but they will eat geese or ducks, and especially in the cold of winter, will find carrion and eat it.

Email Barry Reed at breed71@gmail.com