Butterflies have to rely on external heat sources to warm, so many species migrate to warmer areas such as Mexico, but they can also overwinter in any life stage by releasing antifreeze substances into their bodies.
Overwintering
Overwintering strategies include:
- migration
- dormancy
- hibernation
Migration helps them reach warmer areas in the south and come back north when the weather changes. Dormant butterflies can wake up at any moment when the right temperature hits, while hibernating ones wait for spring.
For example, an adult Red admiral doesn’t enter a full dormancy and can get active on any warmer day. Brimstone, Small tortoiseshell, Peacock, Question mark (Polygonia interrogationis), Eastern comma (Polygonia comma), and Gray comma (Polygonia progne) also overwinter as dormant.
Butterfly Migration
Most butterflies have a short life span and will likely perish within a week, but those that live longer migrate to warmer climates during the winter. Mexico and Michoacán highlands are some of the top overwintering sites.
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For example, the Monarch butterfly lives up to 9 months and is the only US butterfly that has two-way migrations, like birds. As soon as temperature drops and they’re left with no food sources, millions of Monarch butterflies will embark on 3,000 miles road to warmer areas in Mexico and California, close to Santa Cruz and San Diego. Painted lady butterflies, Common buckeyes, and Cloudless sulphurs also head toward warmer climates.
Butterflies in the Winter: Hibernation
On the other hand, some butterflies enter a period of dormancy (diapause) during colder months. During the hibernation process, the butterfly’s body temperature matches the surroundings. Plus, butterflies have specific body chemistry to help them with hibernating.
As days get shorter, butterflies start secreting natural antifreeze (glycerol) into their body fluids. The antifreeze prevents the formation of ice crystals which can rupture cells in the butterfly’s body. About 6 Illinois species, including Mourning cloaks, overwinter as adults. They’ll tuck into crevices in logs and loose bark on trees and begin to appear at the first sign of spring.
They do this in any of the four life stages — egg, larva, pupa, chrysalis, and adult, depending on the species.
Caterpillars in the Winter
Most butterflies hibernate in this form. Species that overwinter as caterpillars bury themselves deep in leaf litter or soil. Caterpillars also enter the state of diapause, where they pump the antifreeze substances into their bloodstream to survive.
The caterpillars will stay near the host plants so they know when spring comes and the host plants start thriving again. Then, they’ll proceed to feed and gain energy, grow, and pupate. For example, Baltimore checkerspot overwinters as a larva. These butterflies also overwinter as caterpillars:
- Great spangled fritillary
- Dreamy duskywing
- Eastern tailed blue
- Juvenal’s duskywing
- Least skipper
Chrysalis in the Winter
Like caterpillars, chrysalis overwinters in a hidden spot, often in deep shrubbery. They’ll release the antifreeze substances, stop their development, and wait for warmer weather to return.
Many Swallowtail species of butterflies (Black swallowtail, Eastern tiger swallowtail, Giant swallowtail) overwinter as chrysalises. They’ll attach to the host plant and wait for the warmer weather. Some other butterflies that spend winter as chrysalis are:
- Delaware skipper
- Hobomok skipper
- Tawny-edged skipper
Butterfly Eggs in the Winter
Finally, some species spend winter as eggs, although they’re the most vulnerable in this form of their life cycle. Adult females will do their best to hide the eggs in the leaf litter at the base of the host plant (aster, milkweed, lumens, birch), usually in the late fall. Those eggs will hatch in the spring once the host plant comes back to life.
One example of butterflies overwintering as eggs is Purplish copper. Adults lay eggs on twigs or leaves, and the eggs stay there the entire winter. Other butterfly species that spend cold months as eggs are:
- Banded hairstreak
- Bronze copper
- Coral hairstreak
- Edward’s hairstreak
- European skipper
- Striped hairstreak
Mileva is a friendly butterfly and nature lover. She enjoys spending time outdoors and getting to know different types of insects, animals and plants. She’s always curious and learning new things, and she shares her love of nature on Butterfly Hobbyist.