Where Do Insects Go in Winter?
As cold-blooded creatures, insects are particularly susceptible to winter’s freezing temperatures. To survive, this class of animals has developed a wide variety of adaptations, including long migrations, creating their own anti-freeze and even purposely freezing portions of their bodies.
Perhaps the best-known migratory insect is the Monarch Butterfly. Each fall, between August and October, this insect packs up (not really) and heads south. Those who summer east of the Rocky Mountains spend the winter in Mexico, while those who summer west of the Rockies winter in California. Unlike most other migratory insects, the Monarchs who return in the spring are the same individuals who left the previous winter. With most other migratory species, including milkweed bugs, Painted Lady butterflies and leafhoppers, when the insects “reinvade the next year . . . it’s different individuals that return.”
Start doing things like putting on extra layers of fat. They also reduce the amount of water inside them. . . . Water freezes at a high temperature compared to other liquids, so they reduce the water and replace it with glycerol, which is similar to the antifreeze we put in our cars.
In addition to making their own Prestone (called cryoprotectants), these insects create an environment in their bodies that is hostile to the formation of ice (ice nucleation), by eliminating its sources, since to create an ice crystal:
Water requires a particle such as dust in order to crystallize and if no source of nucleation is introduced, water can cool down to -42C without freezing.
Taking advantage of this fact, many freeze avoidant insects eliminate:
Ice-nucleating agents such as food particles, dust particles and bacteria, in the gut or intracellular compartments . . . . Removal of ice-nucleating material from the gut can be achieved by cessation in feeding, clearing the gut and removing lipoprotein ice nucleators from the heamolymph.
Although prepping their bodies provides some protection, freeze avoidant insects must also find shelter, and where they winter depends in large part on their stage of development.
Eggs, Pupae and Larvae
Eggs and pupae, which are in a “non-feeding growth stage,” are able to survive at colder temperatures. Some species that winter as eggs include the Praying Mantis and Corn Rootworm, while prominent pupae-wintering species include silkworms, which “may be found attached to food plant branches in the winter.”
Those insects that spend the winter attached to a branch or twig, like the Goldenrod Gall Moth caterpillar, use the plant’s natural defenses to create their winter igloos: as the insect is attaching itself, the plant produces a cancer-like growth in defense, called a gall, which “forms around the insect, shielding it [the insect] from the elements.”
In addition, many species winter as larvae, either in protected cocoons, under “heavy covers of leaf litter or similar shelters . . . [or as] grubs [that] simply burrow deeper into the soil to escape the cold.”
Like those who winter in earlier life stages, adult insects that overwinter in harsh climates, like Mourning Cloak butterflies and bean leaf beetles, also use cryoprotectants and find warm shelters:
In tree cavities, beneath loose tree bark or in unheated buildings. Virtually anywhere they can fit into, to protect them from winter winds and keep them out of the view of birds and squirrels. . . .
Those who snuggle up under tree bark prefer the south side of the tree, where it may be “several degrees warmer on a sunny day.” Ladybugs and box elder bugs, however, generally choose to “overwinter as adults in wall voids, attics, and other out-of-the-way places in homes and other structures,” as do a variety of wasps and flies, including yellow jackets, who are frequently found wintering in the eaves and attics of houses and barns.
Social insects like ants and termites delve down to:
The deep reaches of their underground colonies that extend below the frost line. There, they feast on food they stored during the warmer months.
Another communal bug, bees, have a different adaptation to beat the wintertime cold:
When the hive temperature drops below 64 degrees, honeybees cluster together into a carefully organized, compact ball. The interior bees generate warmth by vibrating their wing muscles. The outer bees are motionless, acting as an insulation layer. . . . The honeybees take turns enjoying the warmth in the middle of the huddle and then move to the outside. Not surprisingly, the queen bee reigns supreme in the middle and never takes a turn on the outskirts . . . .
Despite their strenuous efforts, bee colonies can potentially become completely lost or lose most of their members to the cold of winter.
Some insects don’t enjoy the luxury of sitting the winter out.
Species like mayflies, stoneflies and dragonflies winter as nymphs (an immature stage that resembles the adult stage), and unlike their other relatively sedate cousins, these “feed actively and grow all winter to emerge as adults in early spring.”
Energetic, they are able to “micro-migrate” to warmer water within their environments as needed, and there is evidence that, like their freeze avoidant relatives, they have developed cryoprotectants to lower the temperature at which they would freeze.
Other insects simply cannot escape or hide from the cold and instead have had to adapt to it directly. By far, freeze tolerance is more common in the Southern Hemisphere where there is:
Greater climate variability, where insects must be able to survive sudden cold snaps yet take advantage of unseasonably warm weather as well.
These bugs, including the wooly bear, the alpine cockroach and the flightless midge, all have developed a stark survival method – purposefully freezing selected portions of their bodies, in certain ways and at certain times, to avoid the damaging effects of ice:
Freeze-tolerant insects are known to produce ice nucleating proteins. The regulated production of [which] allows insects to control the formation of ice crystals within their bodies. . . . Even freeze-tolerant animals cannot tolerate a sudden, total freeze; for most freeze-tolerant insects, it is important they avoid supercooling and initiate ice formation at relatively warm temperatures. This allows the insect to moderate the rate of ice growth, adjust more slowly to the mechanical and osmotic pressures imposed by ice formation. . . . Once freezing is initiated, ice will spread throughout the insect’s body.
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