- April 25, 2017
Monarch butterflies are famous for traveling long distances each year, but they’re not the only insects that migrate. Many butterflies, moths, and dragonflies take to the air for seasonal migrations, and–although they’re pretty quiet about it–some travel hundreds or thousands of miles.open_in_new The success of their journey largely depends on the habitat they encounter along the way. Here, we look at some of these six-legged critters and discuss how even the smallest garden can add fuel to their journey.
People were once skeptical that insects could migrate long distances. Historically, scientists assumed an organism so small and short-lived couldn’t move more than a few miles. As we now know, they can. Bogong moths (Agrotis infusa) in Australia can migrate over 1000 km every spring.open_in_new Danaid butterflies (cousins of monarchs) in Taiwan migrate over 300 km in the fall.open_in_new Wandering glider dragonflies (Pantala flavescens) cross the Indian Ocean (the image above depicts a beach in India where migrating dragonflies are coming ashore).open_in_new The brown planthopper (Nilaparvata lugens), a tiny insect only 4 millimeters long, migrates over 200 km in China.open_in_new These are just a few of the hundreds of insect species around the world that make incredible journeys.
By the mid-1900’s scientists finally recognized that insects could move long distances; but still, they assumed insects were being haphazardly blown by the winds, unable to control their direction. In recent years migrating insects like the Silver Y moth (Autographa gamma)open_in_new provided evidence to contradict that theory, showing, instead, that insects selectively choose directional winds to maximize their speed, allowing some to fly up to 650 km a night.open_in_new
Many insect populations have adapted to make round-trip migrations over the course of a year, with the help of multiple generations. Painted lady butterflies, for instance, fly north out of Mexico in the spring to travel to the northern U.S. and Canada; later, their grandchildren or great-grandchildren return south in the fall. Monarchs behave similarly. A handful of insect species engage in single-generation migrations, where the same individual moves during one season and returns a few months later.
In eastern North America there are over 30 insect species that migrate north in the spring and south in the fall. Below we describe a few of these migrating dragonflies and butterflies and we also note the butterfly’s’ host plants (i.e. caterpillar food) to inspire your garden selections.
Common buckeyes (Junonia coenia)
Large eyespots on all four wings make these butterflies easy to identify. In the spring, buckeyes migrate north from Mexico and the southern U.S. They reach the midwest and northeast by May and breed throughout the summer. Male buckeyes will defend territories with host plants to await the opportunity to mate with females. To keep their patch of land, males chase off anything that moves–even birds that enter their territory. In the fall, the next generation of buckeyes makes a massive migration south to avoid a harsh winter of low temperatures and lack of food. Common buckeye caterpillars survive on the leaves from snapdragons (Antirrhinum), false foxglove (Agalinis), American bluehearts (Buchnera americana), plantains (Plantago) and–my personal favorite–turkey tangle frog-fruit (Nodiflora), among other plants.
American lady (Vanessa virginiensis)
These butterflies have an intricate cobweb-like pattern on the underside of their wings. American ladies live year-round in the southern U.S. and Mexico and migrate into the northern U.S. and Canada for the spring and summer each year. Larvae munch on leaves of pearly everlasting (Anaphalis), ironweed (Vernonia fasciculata), and asters (Asteraceae). American ladies are closely related to, and often confused with, painted ladies (Vanessa cardui), which migrate along a similar route in the U.S.
Cloudless sulphur (Phoebis sennae)
Each spring, these yellow butterflies with pink-edged silver spots migrate from Central America and the southern U.S. into the northern U.S. and Canada. Cloudless sulphurs reach the Great Plains by April and the Midwest by May and June. They can be seen gathering at mud puddles to sip water and salt. Cloudless sulphur caterpillars eat plants in the pea family (Fabaceae). Males relentlessly pursue potential mating partners, but uninterested females may reject males by raising their abdomens in the air, much like turning up your nose. In the fall, a later generation of butterflies returns south, sometimes traveling in enormous numbers.open_in_new Sadly, cloudless sulphurs have dropped in numbers since the 1980s in the eastern U.S. Reasons for population declines are not well understood, but habitat loss is a likely cause.open_in_new
Question mark (Polygonia interrogationis)
Question mark butterflies, named for a quirky little “?” shape on the underside of their wings and known for their hooked forewing (a.k.a anglewing butterfly), migrate south in massive numbers in the fall along the east coast. Some of the same individuals are thought to return northward into the northeast in the spring where they reproduce, lay eggs, and start the next generation. Plants that support these caterpillars include elms (Ulmus), hackberries (Celtis), nettle (Urtica dioica), and false nettle (Boehmeria Jacq.), but interestingly the females often lay their eggs on non-host plants and when the larvae hatch, they are tasked with finding host plant species to eat. The question mark is commonly confused with the eastern comma butterfly (Polygonia comma), which also have hooked forewings (a.k.a., anglewings) but are currently not known to migrate.
Mourning cloak (Nymphalis antiopa)
The mourning cloak could just as well be from the wizarding world of Harry Potter as from anywhere. These butterflies look like Potter’s invisibility cloak – and when they close their wings, they “disappear” into a landscape of dried leaves. Mourning cloaks are globally distributed and thought to be the longest-lived of butterflies, frequently surviving 10-11 months. In the U.S., some of these butterflies will migrate into the southeast in the fall while others remain in the north, but little is known about what controls this behavior. The caterpillars consume willow (Salix), cottonwood (Populus), paper birch (Betula papyrifera), elm (Ulmus), and common hackberry (Celtis occidentalis L.).
Red admiral (Vanessa atalanta)
Red admirals are recognizable from the orange-red bands on both forewings. They live all over the world. In North America, they undertake northward migrations in the spring, colonizing the northeast by April. In October, they appear in massive migratory groups of hundreds to thousands of individuals headed south to Texas and beyond to escape the cold. Males are aggressively territorial over important resources (nettle and false nettle) and will chase off potential competitors. Adult red admirals prefer to consume sap flows on trees, fermenting fruit, and can be found collecting salts and minerals from bird droppings. In a pinch, they can also nectar on flowers.
What do sap, rotten fruit, and bird droppings have in common?
Answer: They are all sources of food for mourning cloak, question mark, and red admiral butterflies. The xylem and phloem that make up the “wood” inside of a tree are responsible for transporting water, sugars and minerals important for tree health and growth. When these layers are damaged or there is a buildup of carbon dioxide in the tree, the sap they carry can be forced to the surface and exposed. The sugary, mineral contents of the sap makes for a delicious meal for a few species of adult butterflies. Bird droppings can provide additional nutrients, such as uric acid or other proteins thought to support egg production.
Common green darner (Anax junius)
Green darners are one of at least nine species of dragonflies now thought to migrate each year in North America. Highly recognizable, the green darner has a pale-green face with a darker green thorax, blue abdomen, and clear wings. During August-October these large dragonflies migrate up to 2800 km from eastern North America to southern Texas, and beyond. During this migration, swarms can reach over 1 million individuals. Using small radio transmitters, scientists have tracked these movements and discovered that common green darners can cover up to 140 km per day.open_in_new Not all common green darners migrate; some, in northern locations, will delay pupation and overwinter in the water as nymphs, emerging as adults the following spring.
Wandering glider (Pantala flavescens)
These dragonflies are regular annual migrants in North America, moving from Mexico and the southern U.S. in the summer and arriving into the northern U.S. later than common green darners. They cannot survive the winter in the chilly north, so they return southward in the fall, often traveling at night (presumably to avoid predators). Their pale-yellow face with darker yellow abdomen, dorsal brown stripe, and clear wings make this species of dragonfly easy to identify.
How to Support Dragonflies in your yard
Water habitats like marshes and ponds are important in most dragonfly lifecycles; therefore, to support them in your yard, maintain or build a rain garden, pond, or a wet area and leave the natural water edges wild (no mowing). If water isn’t an option on your property but is close by, let dragonflies feed on wasps and mosquitos, instead of using pesticides and insecticides.
Providing habitat in gardens can go a long way towards protecting these insects and their migrations. Here’s how to make your yard a stopover or breeding site for insect migrants:
(1) Plant host plants for the caterpillars and nectar plants for the adult butterflies.
Visit our Explore tab, type in your zip code under “Local Resources”, and a Pollinator Planting Guide for your region can be downloaded. Use this guide for choosing plants for pollinators. A quick summary of those species highlighted above are summarized below.
(2) Plant native rather than exotic host plants.
Recent scientific studies suggest native plants provide the best support for butterflies. For monarchs, for instance, the natural seasonality of native milkweeds helps to maintain butterfly migration and health. In contrast, tropical milkweed (Asclepias curassavica), an exotic plant not native to the U.S., can grow year-round in some places and has been linked to high infectious disease risk for monarchs. We suggest planting native milkweed like swamp milkweed (Asclepias incarnata) or butterfly weed (Asclepias tuberosa) whose blooms are more seasonally aligned with monarch lifecycles.
(3) Avoid insecticides.
Synthetic pesticides, including neonicotinoids, can kill butterfly caterpillars. Alternatives to synthetic pesticides include insecticidal soaps (such as those from potassium salts of fatty acids), which can be sprayed on plants when no caterpillars are present and rinsed off with water.
(4) Contribute to citizen science.
Much of what we know about butterfly migration is thanks to the help of citizen scientists. Want to help and contribute to these citizen-science projects? Check out Monarch Joint Venture’s Monarch project list.
Scientists have a lot more to learn about insects (including ~5.5 million estimated speciesopen_in_new) and their migrations. In some cases, insect migrations provide ecological services, like nutrient cycling and pollination, which we are only beginning to understand. As we learn more,we can support these insect migrants through gardening in the spring and fall. If you want to pledge to support pollinators and dragonflies, check out our Planning Tool and let us know about your best intentions.
About the author
As an ecologist, Dara Satterfield is fascinated with animal migration and infectious diseases. She investigates these areas through the study of insects, especially monarchs. Satterfield’s mission is to use her research to inform conservation efforts for migratory species and to connect public audiences with wildlife through citizen science. She is currently a James Smithson Post-doctoral Fellow at the Smithsonian Migratory Bird Center, where she is working with Peter Marra and Scott Sillett to examine the diversity and ecological implications of insect migration.