Where do butterflies go in the winter?

As the long, hot days of summer slide into cooler, shorter days of autumn, seasonal changes are occurring in my garden. Not as many plants are blooming, the leaves on deciduous trees and plants are becoming drier and starting to change color. Some plants are producing autumn berries that will sustain many birds as insects, another source of food, begin to disappear.

Quite a few butterflies have been showing up in my garden to take advantage of flowers that are still blooming. Butterflies I have been seeing include painted ladies (Vanessa cardui), common buckeyes (Junonia coenia), fiery skippers (Hylephila phyleus)and cabbage whites (Pieris rapae).

With the advent of winter, butterflies disappear since they cannot tolerate temperatures below 55°F or rainy weather. So, what happens to butterflies in the winter???

Like all insects, butterflies undergo metamorphosis during their life cycle. Stages are from egg to larva/caterpillar to pupa (in chrysalis/cocoon) to adult. Different species have different winter survival strategies, during different phases of their life cycles.

Some Butterflies Migrate

Some butterfly adults migrate south, overwintering in warmer climates.

Monarch butterflies are known for their astonishingly long spring and fall migrations. Both the eastern monarchs and western monarchs began their southern migrations in late August or early September from southern Canada/northern USA to their overwintering sites. The eastern variety generally heads to the oyamel fir forests in the mountains of central Mexico, whereas the western Pacific species have a shorter journey to California's coastline. You may see some western monarchs this fall resting or feeding on flowers in your garden as they fly through the Central Valley on their way their overwintering sites in coastal areas such as Santa Cruz, Pacific Grove, Pismo Beach, and San Diego.

However, monarch butterflies are not the only butterfly species that migrate south. Like monarchs, painted ladies, common buckeyes, cloudless sulphurs (Phoebis sennae) and gulf fritillaries (Dione vanillae) are currently heading to their winter ranges, which are in southern California or western Mexico (including Baja California). However, these butterflies have a much shorter journey than monarchs since they do not journey as far north during the summer.

Other Winter Strategies

Most butterflies spend winter in the same area they spent summer.

Some lay their eggs in autumn on, or close to, their specific host plants with the eggs hatching the following spring. The common hairstreak (Satyrium californica) eggs are laid attached to twigs of oaks with the caterpillars feeding on newly emerged spring leaves.

Some species' caterpillars go into hibernation during the winter season. Duskywing butterflies such as the mournful duskywing (Erynnis tritis) generally have three generations each year with the third generation hibernating as a caterpillar within a tubular retreat formed of rolled leaves tied together with silk strands, sheltering themselves in protected tree nooks and crannies, or leaf litter, and pupating in the early spring.

Some butterflies weather the cold as pupa within a chrysalis in a sheltered spot. During this time, the pupa will enter diapause (where development stops). An antifreeze chemical in their blood allows them to survive cold temperatures. Once the days lengthen, it will resume its transformation, emerging as an adult just as in time for blooming flowers that provide nectar.   The tiger swallowtail's chrysalis (Papilio rutulus) will take refuge in deep shrubbery. The anise swallowtails (Papilio zelicaon) and cabbage whites also generally overwinter as a pupa in their chrysalis. Fiery skippers usually overwinter as pupae buried in leaves, but some adults will migrate to southern California.

Mourning cloaks (Nymphalis antiopa)go into dormancy as an adult. Their blood also contains an anti-freeze. They tuck themselves into cracks and crevices of rocks and trees.

Leaving the Leaves

You can help local butterflies survive winter no matter how they do it by:

• Learn which butterflies live in your area and grow native plants for those specific species.
• Offer nectar plants in the fall and spring months for butterflies that are migrating, emerging from overwintering, or getting ready to go into winter dormancy/hibernation. 
• Skip raking the leaves in your garden in autumn and leave standing plants alone until midspring, so overwintering butterfly larvae, pupae and adults have a place to hide. If leaving the leaves on your lawn is too messy for you, consider not disturbing the leaves in your planters. 
• If you find what looks like a dead chrysalis (many resemble dead leaves) in your yard, garage, shed, do not disturb it. A butterfly may well emerge in the spring.
• Avoid using pesticides as much as possible.

As is happening to other species, climate change, habitat loss, and pesticides are causing these important pollinators of many native plant species to be in trouble. Helping butterflies get through the winter months and the rest of the year will aid their survival and allow them to continue to bring us joy in our gardens with their beauty.

Resources

• Art Shapiro's Butterfly Site: https://butterfly.ucdavis.edu/butterflies
• Butterflies in Your Garden, Publication from UCCE Stanislaus County :https://ucanr.edu/sites/CEStanislausCo/files/345791.pdf
• Xerces Society - Pollinator Plants: Central Valley of California: https://xerces.org/publications/plant-lists/ppbi-california-central-valley 
• California Native Plant Society: https://www.cnps.org/ 
• UC Davis Arboretum – Larval Hosts for Butterflies: https://arboretum.ucdavis.edu/blog/larval-host-plants-butterflies

 Denise Godbout-Avant has been a UC Cooperative Extension Master Gardener in Stanislaus County since 2020.