How do Butterflies Survive Winter?

Have you ever wondered how butterflies survive the cold snows and bitter winds of winter? Most people are familiar with the amazing, long migration of the Monarch butterflies to Mexico to escape the cold, but many species of butterflies hunker down for the winter in your backyard. “The great majority of butterflies stay where they are. They spend the winter where they spend the summer,” says Jeffrey Glassberg, biologist, author and president of the North American Butterfly Association.

A butterfly sits a top a mound of snow. (‘Field Notes’: Butterfly Winter Survival Strategies)

Among the approximately 700 species of North American butterflies there are three main strategies that have evolved for winter survival. The first involves diapause, either as an egg, a caterpillar, or as a chrysalis. Hibernation in the adult form is the second strategy. The third and final solution is simply to head south.

Most butterflies spend the winter months in a condition called diapause. Diapause is a period of suspended growth or development at a particular stage in the life cycle, to protect butterflies from long periods of inclement weather. Onset of diapause is stimulated by reduced daylight hours. Each species that enters diapause will do so in a different life stage: egg, larva, pupa, or adult.

Many species spend the winter as caterpillars such as the Tawny Emperor, Hackberry Emperor, Viceroy, Red-spotted Purple, and many other species.  They create a nest out of leaves and wait until spring to emerge. These nests are called hibernacula (singular = hibernaculum). When spring arrives with longer days and new leaves on their trees, they emerge and begin eating and growing again.

Viceroy and Red-spotted Purple caterpillars cut a leaf to a specific shape after sewing it to the twig. They then lay a layer of silk over the leaf. As the silk dries, it draws the sides of the leaf into a tight roll. The caterpillars stay inside the leaf roll during the winter.

In the winter, the trees will drop their leaves. Caterpillars that overwinter will instinctively first sew their chosen leaves to the twig. Some species simply sew several leaves together or fold one leaf and stay inside during the winter. Some species, such as Tawny Emperors, will change color from green to brown inside their hibernaculum. Brown caterpillars inside brown leaves would be extremely difficult to see.

Swallowtail butterflies spend the winter as chrysalides. Just before they pupate, the longer nights and cooler temperatures will trigger the caterpillar to become a chrysalis and go into diapause. When it starts to warm up in the spring, the swallowtail will emerge from the chrysalis.

Butterflies who spend the winter in chrysalis find a sheltered place like overhangs or deep shrubbery. The chrysalis, like the adult and caterpillar, stops development over the winter months and contains special chemicals to keep from freezing. When the warmer weather returns and the days lengthen, development resumes in the chrysalis and the adult butterfly emerges in time for fresh blooms on nectar plants.

The chrysalis of the Giant Swallowtail hangs from a tree where it is camouflaged from predators but otherwise exposed to wind, snow and sleet. Relatively safe in its little home, the developing butterfly survives without eating or drinking by lowering its metabolic rate to the bare minimum. To keep from freezing, it makes glycerol, which acts as an antifreeze in its blood.

Perhaps the most vulnerable species are those who spend the winter as eggs, usually laid in late fall in the leaf litter at the base of the host plant. These eggs will hatch in the spring when the host plant has put on new growth.

Eggs are situated safely in the crevasses of the tree bark and branches, at the roots of the tree, or in the leaf litter surrounding it.

Butterflies that remain in cold-winter areas as adults find safe places to rest, like tucked into crevices, under or in between logs or underneath loose bark on trees and then will enter into diapause. The butterflies shut down all their non-essential systems like reproduction and slow their metabolism dramatically. Special chemicals in their bodies work as anti-freeze, and the butterfly remains dormant until warmer weather arrives. These species, particularly the Mourning Cloak, often can be seen flying on the early days of spring, and occasionally even during warm spells in January or February.

These butterflies have special adaptations for survival. They prevent damage to their insides by increasing the level of glycerol, a type of alcohol in their blood, and by converting excess water in their bodies into a gelatin-like substance that won’t freeze.

Some butterflies, such as the Monarch butterfly, migrate to warmer climates or travel to overwintering sites. They cannot survive freezing temperatures. Monarchs that overwinter in Mexico and California during the overwintering period (approx. October-March) are usually in reproductive diapause, which means they stop mating and laying eggs.

Overwintering Monarch cluster in Pacific Grove, California.

Many other species migrate to warmer climates for the winter and continue their normal lifecycle pairing and laying eggs, during the winter. Their offspring migrate back in the spring. The Painted Lady is known for its migratory behavior here in the United States as well as its epic migration between Europe and Africa.

You can help a butterfly survive winter, no matter how they do it, with a few simple actions:

Leave the leaves! Leaf litter helps replenish soil nutrients and provides overwintering habitat for a number of beneficial invertebrates. If you can’t leave leaves throughout the yard, consider creating a leaf pile or adding leaves to compost.
Ditch the fall garden cleanup. Besides leaving leaves, consider leaving standing flower and grass stalks in your garden. Sometimes, these stalks harbor chrysalises or pupal cases from local insects like native bees. These areas also provide winter shelter and food for birds. Remove plants in the spring. Generally, by the time the grass needs its first cut in the spring, the pollinators have emerged.
Sow seeds and plan out next year’s garden. Butterflies not only need nectar plants to feed on as adults, but they need host plants for their young caterpillars to feed on as well. Winter is the best time to start planning and preparing your garden for spring and summer butterflies. 

Over-wintering Monarch Butterflies

Monarch butterflies are known for their incredible, long-distance migration from as far north as Canada to their wintering grounds in Central Mexico. But did you know that not all monarchs over-winter in Mexico?

A cluster of monarch butterflies Monarch butterflies in Goleta, California. Monarch butterflies migrate to Goleta each October through February and are best viewed at the Ellwood Main monarch grove. A map is available here.

Monarchs living west of the Rocky Mountain range in North America overwinter in California along the Pacific coast near Santa Cruz and San Diego. Here microclimatic conditions are very similar to that in central Mexico. Monarchs roost in eucalyptus, Monterey pines, and Monterey cypresses in California.

California State Parks is the largest single overwintering site landowner and manages 25 of the 246 overwintering populations. https://www.calparks.org/blog/ideal-home-western-monarch-butterflies

Every Thanksgiving and New Years the Xerces Society along with hundreds of volunteers count the number of monarch butterflies at overwintering sites in the West.

Total monarchs reported and number of overwintering sites monitored for the Western Monarch Thanksgiving Count from Nov. 1997 to Dec. 2022

The South Carolina coast is also home to a winter population of monarch butterflies, according to a recently published study published by South Carolina Department of Natural Resources (SCDNR). The research indicates that the insects live year-round in South Carolina, relying on swamps in the spring, summer, and fall and sea islands in the winter. 

Monarch butterflies  spend winter on surrounding barrier islands in South Carolina instead of migrating to Mexico. The butterflies on rely on Aquatic milkweed (Asclepius perennis) as a host plant for their eggs and caterpillars. Credit: E. Weeks/SCDNR

And then there is Florida! Because of the warm climate and continuous availability of host plants, much of Florida’s monarch population stays in the state year-round and breeds continuously throughout the year. Year-round residents are more common in southern Florida, as cold winter temperatures in northern Florida can kill monarchs at any life stage.

Monarchs can find many flowers blooming in Florida during the winter such as this Mexican Sunflower.

In addition to resident populations, the state also hosts migratory monarchs from northeastern North America, but there are competing hypotheses regarding how these migrants travel to, from, or through Florida.

When I lived in Central Florida I observed that monarch populations increased in late November. According to Dr. Karen Oberhauser, Florida is a terminal destination for migrating monarchs from the northeastern United States and southeastern Canada. These monarchs fly into Florida but don’t disperse out, making the Florida population a “sink population.”

Wherever monarchs are this winter, we can help these iconic butterflies by creating habitat for them in our own back yards. 

Monarchs cannot survive without milkweed; their caterpillars only eat milkweed plants (Asclepias spp.), and Monarch butterflies need milkweed to lay their eggs. Click here or on the photo to purchase milkweed seeds.
Plant Milkweed Pink T-Shirt. Click to check for your size and color preference: https://amzn.to/3R7o0Sy

The Incredible Migrating Painted Lady

Most of us are very familiar with the monarch migration this time of year. But did you know that monarchs are not the only butterflies that migrate? In fact, there is a butterfly that migrates even farther distances than the monarch.

The Painted Lady (Vanessa cardui), boasts the world’s farthest known butterfly migratory route, undertaking a phenomenal 9,000-mile round trip from tropical Africa to the Arctic Circle.

Click here or on the map to download pdf format.

As one of the most cosmopolitan insect species in the world, the Painted Lady is found in all continents except Antarctica and Australia. Some of the reasons for its widespread distribution include a wide variety of plants it feeds and lays eggs on, the ability to migrate to avoid winter, and continuously reproducing.

Butterfly Migration is a global citizen science project tracking Painted Lady butterfly migrations around the world. http://www.butterflymigration.org/

Painted Lady larvae feed on an incredibly wide variety of host plants from many different families including thistles (Cirsium spp.), borage (Borago officinalis), hollyhock (Alcea rosea), mallow (Malva spp.), sunflower (Helianthus spp.), Plantain (Plantago spp.), and a few legumes including soybeans.

The Painted Lady butterfly and some of its host plants. Find seeds here: https://mybutterflylady.etsy.com

The Painted Lady is also known for its migratory behavior here in the United States. The butterflies will set off from their wintering grounds in the Mojave and Colorado deserts of southeastern California as winter gives way to spring. They travel roughly the same path every year, flying northwest to Sacramento in route to Oregon, Washington and beyond. (They’ve been spotted as far north as Alaska.) These migrations appear to be partially initiated by heavy winter rains in the desert where rainfall controls the growth of larval food plants.

In March 2019, after heavy rain produced an abundance of vegetation in the deserts, Southern California saw these butterflies migrating by the millions across the state.

Research on the Painted Ladies in North America is limited, but scientists believe they migrate to the southwestern United States and northwestern Mexico in the fall. They arrive in the desert in late fall and the cycle begins again.

In October of 2017 the National Weather Service took this radar image over Colorado that shows migrating Painted Lady butterflies. https://denverite.com/2017/10/04/many-butterflies-denver-showed-radar/

One of the most interesting Painted Lady butterfly facts is that it can reach a speed of nearly 30 miles per hour, allowing it to travel up to 100 miles per day during its migration.

Some confuse these butterflies with the Monarch (Danaus plexippus). While their color scheme may be similar to Monarch butterflies, Painted Ladies have eyespots on the underside their wings in addition to brown coloring on both sides. Painted Ladies lack the vein pattern that Monarchs are best known for. Painted Ladies are also smaller than Monarchs, with a wingspan measuring less than 3 inches.

The Painted Lady breeds throughout the year. The female lays eggs during its migration, contributing to its global distribution. The butterfly undergoes metamorphosis as part of its life cycle that ranges from 1 month in subtropical areas to 2 months in the temperature zones.

Eggs are laid singly on plant leaves and develop over the course of 5 days, before the caterpillar hatches. Five larval stages, also known as instars, span over 25 days where the caterpillar feeds continuously and grows extensively, followed by a pupation stage when metamorphosis takes place. The adult butterfly emerges from the pupa after a week and finds a mate before settling on a leaf to lay eggs and start the cycle again.

The painted lady butterfly life cycle has four stages: the egg-laying stage, the larval stage, the pupal stage and finally the appearance of the adult butterfly.

Painted Ladies are one of the easiest butterflies to raise because not only will the young larvae feed on so many different host plants, they will also feed on a specially formulated artificial diet.  This artificial diet makes it possible for the larvae to be sold in butterfly rearing kits and are often raised and studied in classrooms by elementary students.

You can order live caterpillars to grow Painted Lady butterflies here: https://amzn.to/3T1OLth

 

Plant Frostweed to Help Migrating Monarch Butterflies

According to Monarch Watch, Frostweed (Verbesina virginica) is a major fall-blooming nectar source for monarchs. By fall it’s usually at least three feet high and has dense clusters of snow-white flowers. Blooming typically coincides with peak migration.

This native plant is an important pit stop for Monarch butterflies’ fall travel. https://journeynorth.org/monarch/fall2013/c101013_frostweed.html

The blossoms are also attractive to many other species of butterflies, bees, and other pollinators. It is the host plant for the Bordered Patch (Chlosyne lacinia) and the Silvery Checkerspot (Chlosyne nycteis) butterflies.

Laviana skipper (Heliopetes laviana), Bordered Patch (Chlosyne lacinia), White Peacock (Anartia jatrophae) and Tropical Checkered-Skipper (Burnsius oileus)

Native to the Southeastern United States and Texas, Frostweed is perennial throughout USDA zones 6-9. Reaching an average height and spread of about 3 feet, this plant is ideal for cottage gardens, background plantings in shady garden borders, or naturalized in wooded areas. 

Click here to purchase seeds.

The name “Frostweed” is a reference to the plant’s tendency to excrete water from its stems in freezing weather, thus enhancing the winter landscape with the creation of interesting ice sculptures. Frostweed (Verbesina virginica) it is also known by other names including White Crownbeard, Indian Tobacco, Iceplant, Iceweed, Richweed, Squaw Weed, White Wingstem, and Virginia Crownbeard.

Frostweed after the season’s first freeze, a phenomenon known as crystallofollia.

Growing tips: Frostweed prefers dappled shade where it can form sizable colonies, like at the edge of a woodland or just under a large tree. Plant your Frostweed in a naturalized area where it can get dry to moist soil. It will grow from 2’-6’ tall with little to no maintenance, irrigation or pest control. If you plant it in a dryer and sunnier space you will tend to get smaller and more compact bushes with more flowers. You can also promote more fall blooms by cutting back the plant in mid-summer.

Aphids!

If you grow milkweed, you will most likely have aphids. I constantly get asked, “How do I get rid of the aphids on my milkweed?”

Oleander aphids infest many milkweed species including common forming large colonies of bright yellow aphids with black cornicles and legs.

Aphids are a non-native insect and they can multiply very quickly. However, they are not a direct threat to monarch caterpillars because they feed on the milkweed plant only. They can indirectly affect caterpillar health by depleting nutrients in their only host plant. They tend to be problematic when the plant is very small or weak. Aphids suck sap from the plant tissues, and if populations are high, can stress plants and kill small or young plants.

Heavily infested milkweed can be stunted or deformed, and black sooty mold grows on the large amounts of sticky honeydew produced by the aphids. When aphids or other sap sucking insects suck sap from a plant, the plant is weakened and there is a risk of the insect infecting the plant with disease. It sometimes spreads plant viruses from one plant to another.

This common milkweed has been infected with the aphid-borne virus called “Yellow Virus”. Photo by the BugLady.

I do not recommend using insecticides to control aphids because it will kill much more than the aphids and most likely your monarch larvae as well. Even if the insecticide is labeled organic, that doesn’t mean it’s safe for caterpillars. Using systemic insecticides to get rid of aphids can be much more harmful to the monarch caterpillars than the aphids themselves. Some people recommend using neem oil but the oil tends to stay on the leaf. Neem oil can also be systemic. One label states that “neem oil does not harm beneficial insects, only sucking and chewing insects”. Caterpillars are chewing insects.

Here are some recommended strategies to help control the aphids population on milkweed:

  • If there is enough milkweed for caterpillars, cut off any part of the plant that is infected with aphids and dispose of the stems in a sealed bag.
  • Although time-consuming, the safest way to remove aphids is manually by squishing them between your fingers (you can use gloves to avoid staining your fingers) and then using a hose to dislodge them from the plant. I use this method with young milkweed plants. It is best to catch the aphids before they become an aphid army, so even if there are just a few on the plant, remove immediately.
  • The easiest way to control aphids is to use the hose to blast them off every couple of days. You won’t completely get rid of them, but it helps. The negative side is that it does not remove all the aphids or kill the aphids. Some of the aphids may find their way back to the plant. For this method to work you need to do this frequently.

  • ​If you have a severe infestation of aphids on the milkweed you can use a soapy water solution.  The soap solution should be sprayed either in the early morning or late evening. In bright sunlight, soap acts as a magnifying glass and the light burns the leaves, sometimes causing the plant to drop all leaves.

Here is the recipe recommended by Monarch Watch: mix 1 gallon of water with 1-ounce of Blue Dawn dish soap, 1-ounce isopropyl alcohol, and 1-ounce white vinegar and pour into a spray bottle. Saturate the plant with the soap solution and allow the plant to sit for 10-15 minutes, then wash off with a hose. Both the tops and bottoms of the leaves should be sprayed and rinsed. Be sure you remove any caterpillars or eggs before applying!

  • Beneficial insects are great for controlling aphids because they rarely harm monarch eggs, caterpillars, or adults and once introduced, they take no effort on your part! There are many species of beneficial insects. It is important to be able to identify these insects so you know which ones are on your side. Ladybugs, hover flies, lacewings, parasitoid wasps, and a few more types of beneficial insects devour aphids.

    Many natural enemies including ladybugs, hover fly larvae, and parasitoid wasps as well as lacewing larvae will help control the aphis population on milkweed.

After battling aphids for years, I have come to peace with these little yellow critters. For the most part, I just leave them alone (with the exception of young seedlings and plants) and to my surprise Mother Nature comes to the rescue!

An adult Ladybug and the larva of a Hoverfly are feasting on aphids on this giant milkweed.

A recently released study suggests that monarchs are more likely to survive on milkweed shared with non-predatory insects than on a “clean” plant. They believe this is because the plant has more food options for a predator, which lessens the chance that they go after the monarch. So maybe the best strategy is to leave those little orange milkweed aphids alone.