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Where Do Bugs Go in Winter? - December 17, 2017

 

The winter season is creeping closer and closer, and with it comes darker days, colder temperatures, and the ever-present threat of frost and snow. As the skies turn grey with foreboding, and nature columnists wax poetic on metaphors about the weather, residents of the Coastal Bays prepare for the coming freeze. Some of our more auspicious residents make their own seasonal migrations, retreating to winter nesting grounds in sunny Florida. The rest of us can draw the shutters, crank up the thermostat, and hum “Let it Snow” to ourselves as we bask in the warm electric glow of the great indoors.

Instead of curling up in front of the fire, the wildlife of the Coastal Bays must deal with Mother Nature at her most malcontent. Some, like many birds, take a page from those part-time Floridians and hightail it out of here, marathoning thousands of miles on tiny wings for warmth in a more hospitable portion of the hemisphere. Some, like bears and snakes, “sleep” it out, slowing their heart rate and other body functions to a crawl, hibernating (or “brumating” if you’re a reptile) through the hard winter months. The toughest of them, like white-tailed deer, rabbits, and squirrels, grow a thicker coat of fur and muddle through the snow.

But what about bugs? 

In spring, summer, and fall, insects, arachnids, and other arthropods are everywhere; crawling through the grass, buzzing in the air, eating each other, and even eating you, these integral parts of the ecosystem seem to suddenly vanish at the end of autumn. While many of us may feel that this is the best part of winter, it still begs the question: Where do they go?

The answer is remarkably varied, but most bugs follow the same general guidelines that other animals do; they migrate south, hunker down, or try to tough it out. The biggest difference is the way that insects and other arthropods tackle these challenges.

Migrating insects face the same physical challenges that other organisms do, with the added caveat that most insect’s lifespans just aren’t long enough to complete the journey. Monarch butterflies (Danaus plexippus) complete the most famous insect migration; these incredible butterflies flap their way from summer breeding and feeding territories in the northeastern U.S and Canada, over 3,000 miles to southwestern Mexico. Yet, no individual monarch travels this full distance. Those butterflies die on the way back the next year, and their offspring continue the voyage. Often, at least four generations of butterflies are needed to complete the cycle. The green darner dragonfly (Anax junius) travels just as far, all the way to Mexico to avoid the winter chill. Worldwide, many species of dragonfly perform grand migrations, some even farther than the Monarch’s, but little is known about this vast topic.

For those that stick around, temperature is the biggest threat. Since insects are ectotherms (meaning they don’t produce their own heat), and can’t grow a thicker coat to keep warm, they must find a different way to stop from freezing solid. Most bugs combat this problem by stocking up on fat, then winterizing their bodies. The adult or larval arthropod finds a good place to sleep out the winter, like under bark, leaves, or deep in soil, then floods its body with antifreeze, usually a compound called glycerol. Some species, like the wooly bear caterpillar (Pyrrharctia isabella) can even survive being frozen nearly solid by controlling where ice forms in their bodies with special proteins. Next the bug goes into a sort of hibernation, called diapause, in which development stops and metabolism is drastically lowered. With the return of warmer temperatures, the bug “wakes up” from its state of suspended animation and returns to eating and being eaten.

Many insects have decided to not worry about this whole “surviving winter” thing and simply die when the weather turns sour. Bugs like praying mantises, crickets, and some moths only live for around eight months in the wild. Their adult life is a whirlwind of eating, mating, and laying as many eggs as possible, before perishing in the cold. The eggs or pupae of these species go into diapause instead, overwintering like daffodil bulbs to emerge next spring and start the cycle anew.

Very few bugs have adapted to meet the cold head on, which is why they really seem to vanish after fall. In Maryland there are only two major types of winter-active bugs: one species of snow cranefly (Chionea valga), and the springtail snow fleas (genus Hypogastrura); which aren’t insects at all, but are members of subclass Collembola (Collembolans are tiny organisms with internal mouthparts and a powerful lever-like “tail” used to fling themselves out of harm’s way). These bugs can be found walking, or springing, across the snow on warmer winter days, and use the same glycerol antifreeze to fight the weather. The winter stoneflies (families Capniidae and Taenioptergidae), which emerge as adults from their water-bound nymph stage to mate at the end of winter, can also be seen walking across fallen Maryland snow, but they spend the coldest parts of the season hunkered down at the bottom of a stream. 

Take your pick: A 3,000-mile journey, embalmment with antifreeze, or passing the reigns and hoping your kids make it to spring. No matter what you choose, it’s tough being a bug in the dead of winter. You may not like bugs for the rest of the year, but you can certainly appreciate the incredible ways they have found to survive.

At the very least, it gives you a new appreciation for central heating.

 

Patrick Simons is a Seasonal Scientist with the Maryland Coastal Bays Program.



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