Summer wildlife disappear in winter, but where to?

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The end of winter trumpets the arrival of spring and then summer. Our yards green up, flowers bloom and there’s a bustle of animal activity from belowground to the sky. Day or night, it’s non-stop . . . then it stops! Most of the summer wildlife disappear in winter, but where to? If you’ve ever wondered, here are some answers.

How mammals disappear

Mammals are still around. But they spend more time sleeping in their dens, conserving energy and staying warm, surviving off the extra body fat they packed on in the fall.

Skunks remain in their dens for weeks at a time, and several females often share the same one. Raccoons also sleep for weeks or months. Den sites for both animals include such places as abandoned buildings, rock crevices, abandoned burrows of other animals, and for the raccoon, tree hollows.

All about the Striped Skunk   All about the Northern Raccoon

Virginia Opossum facing the camera with bare toes showing and a snowy background.

Winter is hard on Virginia Opossums because they lack hair on their tail and toes. (© Sleepy Joe / Shutterstock)



Winter is hardest on Virginia Opossums, as they lack a thick insulating coat of hair and their tail and toes are bare. Their tail is especially susceptible to frostbite. So, they stay in their dens in miserable weather and forage for food once it warms up. To help insulate themselves, they line their dens with dry grass and leaves.   All about the Virginia Opossum

Tree squirrels may be seen out in the winter, but they spend a lot of time sleeping in their nests, sometimes for days when it’s frigid. If the temperature isn’t too low, they venture out to find food, mainly the nuts they buried in the fall. As for ground squirrels, they hibernate in their den through the winter.
When snow covers the ground   All about Fox Squirrels and Gray Squirrels

Bats spend the winter in hibernation. Most bats are insect-eaters and insects aren’t available in the winter, so colonies disappear into places like unused buildings, old tree hollows, house attics, and caves. They awaken periodically through the winter to relieve themselves but don’t leave their shelter. In March, as the weather gets warmer, bats begin to emerge from hibernation. By April, most are out flying at night, but should the weather cool down, they become inactive again. By May, they’re fully active.   All about bats

Birds stay visible, but sometimes far away

Birds are the year-round constant in our yards, although the species may vary with the seasons. Northern Cardinals, Downy Woodpeckers, and chickadees, for example, are year-round residents, but many others have migrated for the winter. Half of North America’s six hundred fifty breeding species migrate. Some move short distances, from a higher to a lower elevation just a state or two away. But, more than half migrate to Central and South America.

Common Poorwill, Phalaenoptilus nuttallii, lying on the ground.

Common Poorwill, Phalaenoptilus nuttallii. (Gavin Keefe Schaefer / Wiki; cc by 2.0)



Common Poorwills, Phalaenoptilus nuttallii, are distinctively unusual birds, being the only ones that are inactive in the winter. Tucked into piles of rocks, they remain there for extended periods—from weeks to months—in a state of “torpor,” a sleep that’s not quite as deep as true hibernation. Their cryptic plumage keeps them well hidden.   All about birds

Some butterflies migrate, others hibernate 

Most butterflies and moths hibernate in a caterpillar or pupa stage near their host plants. They may tuck into crevices on tree trunks, attach themselves to sturdy plant stems, or even adhere to the side of a building. Many burrow into leaf litter, debris or soil. Some species, such as tortoiseshell and anglewing butterflies, hibernate in their adult stage.

Nearly everyone knows about Monarch Butterflies and their annual fall migration to Mexico, where it’s warm all winter. Less well-known is that around a million Monarchs hibernate in the United States, in and around Pacific Grove, California.

Monarchs migrate for two reasons: They can’t survive cold winters. And the only host plants their larvae will eat—milkweeds—don’t grow in their hibernation areas. So, they must travel to where these important plants are plentiful. (By the way, milkweed species everywhere are under siege from farming and logging operations and human development, a severe threat to Monarch survival. So, be sure to find a place in your yard for milkweed plants.)
Monarchs begin their spring migration northward in late-February and arrive at their northernmost summer areas in late-May and June. Flocks in California migrate to the north and east but remain west of the Rockies. (Southern Florida has Monarchs, too, but they’re year-round residents.) Monarchs that hibernated in Mexico begin an incredible trip north, 2,500 miles long (4,023 km). Successive generations of them fan out across the northern US and southern Canada, staying east of the Rocky Mountains.  Monarch life cycle in pictures
Painted Lady Butterfly (Vanessa cardui), a species that migrates periodically.

Painted Lady Butterflies (Vanessa cardui) also migrate. (Esin Üstün / Flickr; cc by 2.0)



Monarchs are the best-known migrating butterflies, but there are others, including Red Admirals, Cloudless Sulphurs, Gulf Fritillaries, and Common Buckeyes. The pretty Painted Lady Butterflies migrate, too, and don’t hibernate. Constantly on the go, they’re one of the most widespread species, you probably see them in your butterfly garden every summer.

Isabella Tiger Moth (Pyrrharctia isabella), which hibernates as a caterpillar known as a Wooly Bear.

Isabella Tiger Moths, Pyrrharctia isabella, known as Wooly Bears, hibernate in a cocoon.(IronChris / EOL; cc by-sa 3.0)



Other insects

All insects are cold-blooded, meaning they’re unable to regulate their body temperature to stay warm, as mammals do. Freezing weather would kill them. So, depending on the species, they use various tactics for survival. They put on fat to carry themselves through the winter, reduce the amount of moisture in their bodies, and bury themselves. Some, such as the Praying Mantis, hibernate as eggs.

Honeybees stay in their hives through the winter. They don’t hibernate in there—they cluster together and flutter their wings and shiver to stay warm. Their food is the honey they stored in there through the previous summer. If a winter day reaches about 65°F (18°C) or higher, they might leave the hive to forage for any nectar they can find.  All about honeybees

Large cluster of hibernating ladybird beetles, unidentified species.

Hibernating ladybird beetles. (Doctor Popular / Flickr; cc by-sa 2.0)



Many other insects also hibernate as adults. Ladybird beetles (ladybugs) pass the winter hibernating in huge, tight clusters in hollow logs, crevices, under leaf litter, and sometimes inside houses or attics. Ants hibernate underground. Some flies remain active through the winter, but the ones we notice most in the summertime—the bigger ones—hibernate in cracks and crannies.

Most insects hibernate in an immature stage—as an egg, larva, nymph or pupa of parents who have already died. They’re hard to spot, but all around us—in the ground, in rock piles, woodpiles, under tree bark, attached to plants, under the lips of flowerpots, under the eaves of our homes, in sheds, under tarps, or any other place that offers some protection.

Hibernating toad, partially seen in its hiding place.

Hibernating toad. (© WIJIT / Shutterstock)



Frogs and toads

Frogs and toads spend the winter hibernating in protected places, such as caverns, abandoned burrows, a crevice in a log, under a rock or leaf litter, or anywhere else they feel safe. Some hibernate up to eight months. Aquatic frogs hibernate underwater, lying on top of the mud at the bottom or partially buried. Wood frogs are known for their ability to freeze hard as a rock and still re-animate when temperatures warm up.
Watch frozen wood frog awaken   All about frogs and toads

Earthworms

It may be surprising to think of earthworms as migrators, but some are! Like insects, they can’t regulate their body temperature and won’t survive freezing weather. So, they go south in the winter and north in mid-spring. That is, if you think of south as “down” and north as “up.” They move down below the frost line to avoid freezing and upward when the soil becomes warmer. Some species always stay close to the surface and, as a result, die in the winter. However, they leave eggs, encased in tiny cocoons to protect them from freezing and drying, that will hatch in the spring.   Watch earthworms hatching

Nightcrawlers are the largest of the migrating earthworms. They remain relatively inactive in cold soil and become active as the soil warms up. They’re most active once soil temperature rises to 50 to 60° F (10 to 15° C) You might see them in the winter during unseasonably warm weather, but they move back down when the soil turns too cold again.   All about earthworms   Attract earthworms to your yard

Snails

Many snail species hibernate in winter. They tuck themselves into crevices, under rocks and leaf-litter, or other places where they’ll be safe from freezing temperatures. They seal the opening of their shell with mucus to keep them moist (drying out will kill them). Their heart slows from about 36 beats per minute to only three or four and oxygen use is reduced to 1/50th of normal. Often, several will hibernate together. Snails sometimes emerge on very mild winter days.   All about land snails

Two large, brown snails with white-colored epiphragms sealing their openings.

Hibernating snails seal their opening with an “epiphragm,” a layer of dried mucus. (© Victoria Tucholka / Shutterstock)



Spiders

Indoor spiders are there year-round, even though we may not notice them. Some outdoor spiders die in the winter after leaving behind sacs filled with eggs that defy frigid temperatures.

Egg sac of an orb-weaver spider.

Orb-weaver’s egg sac. (L Church / Flickr; cc by 2.0)



Other species spend the winter as young spiderlings that hatched before winter, but they remain clustered together in their communal egg sac until spring. Some wolf spiders spend the winter as nymphs and become adults in the spring. Still others, such as tarantulas and fishing spiders, hibernate as adults under the bark of trees, in cellars, or any other place that protects them. They’ll sometimes awaken and roam around on warm winter days in search of hibernating insects to eat.    All about spiders

* Composite image at top of the page is composed from Creative Commons photos by these photographers — clockwise, from top/left: J JCadiz, Neil McIntosh, MrLebies, Bob Ireton, Skeeze, John Flannery, sparkielyle

More reading:

Cover provides safety, shelter for wildlife    
Basics of a backyard wildlife habitat    

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