Overview 
Butterflies and moths use a variety of strategies in nature to get them through a time of year when cold and lack of food sources may hinder their life cycle. However, in the Haven we are tricking the butterflies into believing it is always summer by keeping it nice and warm for them. We are also using timed lighting to prolong the illusion of daylight.
Hibernation
Hibernation is much like sleeping. The metabolism of an animal slows down enabling it to conserve and survive on very little energy. There are examples of butterflies that hibernate at each stage of butterfly metamorphosis. Many insects, like the Banded Hairstreak butterfly, survive the winter as dormant eggs. Viceroy larvae burrow underground or roll into a leaf tube and crawl inside. Adult butterflies like Mourning Cloaks, Question Marks and Commas hibernate in log piles, under bark and in crevices. Many butterflies, like the Gray Hairstreak, Cabbage White, Checkered White and some swallowtails, spend the winter in their vulnerable chrysalides using the energy stored from their larval stage and avoiding warm weather predators.
Butterflies in the Chicago area do not spend the winter in an active state. Each species uses a different strategy to cope with cold winter weather. Some species do not survive northern winters at all. The Monarch is the only North American butterfly that migrates south at the end of summer. Other species, like the Painted Lady, die off in the northern parts of their ranges each winter. As the weather warms in the spring, these species fly north and lay eggs, recolonizing colder areas like the Chicago region during the summer.
Butterflies that remain in the north through the winter months must cope with the extreme cold of winter during their hibernation. These butterflies produce substances in their eggs or hemolymph (blood), such as glycerol or sorbitol, that act as antifreeze. Each species has evolved to use only one life stage:
egg, larva, chrysalis, or adult for hibernation:
Hibernation as eggs
Many hairstreak butteflies, such as the Coral Hairstreak, pass the winter as eggs.
Once the eggs are laid by the female, they do not hatch until they experience increased day length after prolonged cold period.
|
Hibernation as larvae
Many species hibernate as larvae. The caterpillars often burrow underground for the winter. In other species, like Viceroy and Red Spotted Purple, the caterpillars roll a leaf into a tube, fasten it to a twig and crawl inside. In the spring, the young caterpillar comes out of this hibernaculum and resumes eating and growing.
|
Hibernation as pupae
Other butterflies and many moths spend the winter as pupae. The Gray Hairstreak,
Cabbage White, Checkered White, and several swallowtails spend their winter as chrysalides.
|
Hibernation as adults
A few species hibernate as adult butterflies. Mourning Cloaks, Question Marks, and Commas take shelter in log piles, under loose bark on trees, and in building crevices. On warm winter days, it is sometimes possible to see these butterflies flying about.
|
|
Migration
They fly to where they can benefit from warm sun and blooming host plants. Monarch butterflies are the most famous migratory insects. Other migrating butterflies include Giant Swallowtails, Cloudless Sulphurs, Buckeye, Snout Butterflies and Little Yellows.
Monarch Migration
No life stage of the Monarch can survive winter temperatures in the Midwest. Rather than coping with northern winters, Monarchs have evolved a strategy
of migrating to milder climates. Only the last of several summer generations migrates. When daytime temperatures drop below 60oF, the
butterflies begin to congregate in groups, preparing to fly south. Monarchs from the western region of the country migrate to the coast of California, where they spend the winter roosting in trees in scattered groups from Los Angelos to Monterey. Small numbers of Monarchs from eastern populations may migrate to the Atlantic coast from South Carolina to Florida, to the Gulf coast of Florida, or to Cuba or other islands of the Caribbean. Most of the eastern Monarchs migrate to the highlands of Mexico.
The Monarch's migration southward involves flights of up to 2,500 miles. Individuals travel between 20 and 50 miles per day. Migration occurs during the day. At night the migrating butterflies roost in trees sometimes in larger numbers. Navigation is often along shores and rivers. However, Monarchs also use the sun as a navigational aid.
Migrating Monarchs are in a state of suspended development (reproductive diapause) when they fly south. Although they do not reproduce during the migration, they pause to take noursishment at the abundant late summer flowers that they find along the migration route. Adult monarchs that migrate to Mexico may live up to six months, in contrast to the non-migrating summer generations that live only nine to twelve days as adults. In Mexico, just
10 small patches of fir trees in the mountains are the winter roosting sites for millions of butterflies. The density of the butterflies is so great that
their weight can break off branches from the fir trees where they roost.
In the spring, Monarchs resume reproductive development in Mexico, reach maturity, mate, and start to fly north. Female Monarchs lay eggs as they travel north. Progeny of this generation continue the northward migration. Very few, if any, of those that flew south complete the return journey.
|
