How Insects Survive the Winter
With cold winter weather surrounding us, daydreams often shift to the spring to come – bees buzzing, butterflies fluttering, fireflies flickering, and crickets chirping. Even nibbling mosquitos might be excused, a small price to pay for sunshine and warmer weather. But where are all of those insects now? Are they all dead? Are they napping under the snow? Winters in New England seem harsh enough to us, and we have furnaces and down jackets to protect us. How do such tiny creatures survive the cold, the snow, and lack of food? As it turns out, evolution has provided insects with a bevy of adaptations to not only survive the winter, but to thrive.
Take a look out the window. February’s dominant colors are white and brown – contrasting to the summer’s celebration of green. While a few evergreen plants retain their needles through the winter, their chemical defenses thwart most insects. The rest of the trees, all deciduous, dropped their leaves in the fall to retain water and nutrients through the short winter days. The thermostat has been oscillating above and below freezing, with occasional bouts of snow or freezing rain. There are myriad ways to deal with these wintery conditions, which fall into two major categories: cold avoidance, and cold tolerance. For insects, these methods may occur in the egg, larval, pupal, or adult stage. Here are a few of their stories.
The egg stage is an infrequent overwintering tactic, since insect eggs are so small and delicate, prone to desiccation (drying out). Yet with the proper egg armaments, it can be a winning strategy for tolerating winter conditions. Praying mantis species (Mantis religiosa or Tenodera sinensis) are a famous example, with their ootheca (foamy egg case) sometimes appearing as surprise ornaments on Christmas trees – and sometimes hatching to hundreds of little guests indoors! The babies are fooled – the warmth in your home must mean spring has sprung. Another charismatic insect, the northern walking stick (Diapheromera femorata), tries a different approach – each egg is surrounded by a thick waxy coating, making them look and feel like a tough plant seed. The mother stick insect lays her eggs while still up in the trees, letting the little eggs drop to the forest floor and nestle amongst the leaves for the winter. For both of these insects, the life cycle is simple: lay eggs in the fall, the adults perish, and offspring hatch in the spring.
Many insects overwinter in the juvenile stage – as larvae or nymphs. This is the life stage most likely to make sojourns out into the world on sunny winter days, looking for scraps of food between naps in the leaf litter. You might see the famous wooly bear caterpillar (Pyrrharctia Isabella) on a jaunt, or a cutworm caterpillar (Noctua pronuba) crawling across the snow. Under the ground are busy beetle grubs, shielded from the elements by the insulating power of the soil. And under the water in streams and ponds, despite the chill, you can find a variety of aquatic nymphs going about their lives – mayflies, stoneflies, dragonflies, and more.
Most moths in our area are currently snoozing in cocoons. They do not go through classic “hibernation”, like mice and bears. Instead, they undergo diapause – a temporary suspension of growth. Some hurry up and form into adults in the fall, then wait to emerge in the spring. Others remain a soupy mess until the final push to grow wings and antennae just before emerging in the spring. If you look around the bare branches outside, you might see rolled up clusters of leaves tied together with silk. Those are the cocoons of silk moths – like the luna moth (Actias luna) and cecropia moth (Hyalophora cecropia). If you break off a branch and keep it safe in a cool place like a shed or garage, in the spring you may be greeted by one of our largest and most charismatic insects!
For some insects, it is advantageous to overwinter as an adult, with the ability to scramble and find the best possible location to stay safe and warm. Some of these end up in our homes because we have created the ideal conditions for them! Think about the unwelcome guests you have tried to evict from your home – ladybugs (Harmonia axyridis), stink bugs (Halyomorpha halys), and squash bugs (Leptoglossus occidentalis) – they seem to appear out of nowhere in the fall and try their hardest to stay all winter. Out in the wild, they look for tight cozy spaces in logs, leaf litter, and rock piles. What’s not to love about a window ledge releasing enticing warmth into the cool air? Not creatures to leave their countrymen behind, many of these stinkers are known to release “come join the party” pheromones, inviting all of their friends to accompany them in the newly found paradise (which may be your kitchen). While annoying to have around, they are harmless.
Other adult insects are less altruistic and cuddly – so they must survive the cold on their own. The mourning cloak butterfly (Nymphalis antiopa), along with some other butterflies in the family Nymphalidae, find cozy crevices in which to hide for the winter. They also have a secret superpower, an ability shared with some fish and frogs – they produce glycerols in their blood, which act as an antifreeze. This allows them to tolerate cold temperatures, and be one of the first butterflies active in the spring. But while these butterflies try to tough it out, others would rather take a hike. The most famous method of cold avoidance is displayed by the monarch butterfly (Danaus plexippus) – they migrate! In one long journey, the monarchs from eastern North America fly upwards of 3,000 miles to gather in Mexico for the winter. Interestingly, those adults don’t make it back here in the spring – they have several short generations on the journey northward, so the great-grandchildren of the migrating butterflies actually make it to Connecticut.
There are many other overwintering techniques used by insects – either to avoid or tolerate the cold temperatures that the season brings. If you take a little time poking around the outdoors (or even indoors!) you may find the creatures you thought were “gone”. Hiding under a rock or log, cozied up under the siding of your house, nestled under a flower pot, keeping warm in a closet, or lurking at the bottom of a birdbath. They might be waiting as a tiny egg or an unrecognizable larva. Evolution has resulted in a vast array of physical and behavioral adaptations to deal with the winter months, many of which we are still discovering. In the meanwhile, go ahead and enjoy your own behavioral adaptations - wrap yourself in a fuzzy blanket and turn up the heat!
ABOUT DR. ZACHARCZENKO:
Brigette Zacharczenko is a science teacher at Talcott Mountain Science Center & Academy. She received her BSc in Zoology from McGill University (2010), and her PhD in Entomology from the University of Connecticut (2017). While she loves bugs, she's passionate about all the world's creatures! She teaches a variety of topics at Talcott Mountain Academy including Ecology, Biodiversity, Genetics, Botany, Anatomy, Cell Biology, and Marine Science. At our Science Center, she teaches hands-on biology courses for our summer, vacation, and Saturday programs. When she's not concocting creative science lessons, she is finding new ways to combine science and art.
Sources and further reading:
Where Do Insects Go in the Winter? (Smithsonian)
Insect overwintering (Amateur Entomologists’ Society)
Insect overwintering in a changing climate (Bale and Hayward, 2010)
Insect adaptations to cold and changing environments (Danks, 2012)
Migration and overwintering (USDA)
The myth-busting mourning cloak (Mass Audubon)
Insect Dormancy: An ecological perspective (Danks, 1987)