Migration is a fascinating phenomenon seen in many species of butterflies and moths Every year, these insects embark on incredible journeys across continents and oceans in search of food, breeding grounds, and favorable weather conditions. While migration was once considered rare in insects, we now know it is a regular part of life for many Lepidoptera species
Why Do Butterflies and Moths Migrate?
Butterflies and moths migrate for a variety of reasons
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Food availability – Many species time their migration to track the growth cycles of their host plants. When food sources become scarce in one area, they move to another location where plants are actively growing.
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Breeding – Some species migrate to reach optimal mating and egg-laying habitats.
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Weather – Seasonal changes in temperature, rainfall, and daylight hours trigger migratory instincts. Flying to warmer or cooler climates helps butterflies and moths survive.
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Predator avoidance – Migrating allows populations to escape peak seasons of predation. Moving to new areas helps minimize losses to birds, bats, and other predators.
Incredible Migratory Journeys
Some of the most amazing migratory butterflies and moths include:
Monarch Butterfly
The monarch butterfly (Danaus plexippus) is the most famous migratory insect. Eastern North American monarchs fly up to 3,000 miles each fall to reach their overwintering grounds in central Mexico. Western monarchs migrate to coastal California. The journey takes several generations to complete.
Painted Lady Butterfly
Painted ladies (Vanessa cardui) make one of the longest insect migrations on Earth. Populations breed in North Africa and the Middle East and fly north to Europe in the spring. Some reach Iceland and Scandinavia. In fall, their offspring return south, traveling over 4,000 miles roundtrip.
Bogong Moth
Every spring, millions of bogong moths (Agrotis infusa) migrate from southeastern Australia to the Australian Alps. They aestivate in caves and rock crevices over the summer. In fall the moths return to lower elevations to breed before dying. Their impressive journey covers over 600 miles each way.
Mourning Cloak Butterfly
The mourning cloak (Nymphalis antiopa) overwinters as an adult butterfly in tree cavities and other shelters. In early spring, mourning cloaks become active and migrate northwards, tracking the emergence of their host plants. Some populations fly over 1,600 miles from the southern U.S. to Canada.
Variegated Fritillary
Variegated fritillaries (Euphydryas aurinia) live in scattered colonies across Europe. In fall, populations from Scandinavia migrate south to the Mediterranean region. Other groups fly from mountainous areas to nearby lowlands. Their flights range from 30 miles to over 310 miles.
Death’s Head Hawkmoth
The African death’s head hawkmoth (Acherontia atropos) is a remarkable long-distance migrant. It flies from sub-Saharan Africa across the Sahara Desert and Mediterranean Sea to reach southern Europe each spring. Individuals may journey over 1,860 miles.
Silver Y Moth
In Europe, the silver Y moth (Autographa gamma) migrates in multiple generations over 1,500 miles from southern areas to Scandinavia and northern Russia. Their offspring make the return trip south in fall. Some cross the English Channel or North Sea.
Diamondback Moth
Diamondback moths (Plutella xylostella) are major crop pests with a remarkable migration ability. Populations routinely fly 620 miles between southern Canada and the northern U.S. in a single generation. Longer routes exceed 1,860 miles over the moth’s 4-6 week lifespan.
Red Admiral
Every spring, red admirals (Vanessa atalanta) migrate north from the Mediterranean region and North Africa to breed across Europe. In fall, new generations fly south to overwinter. Journeys between northern Europe and the Mediterranean exceed 1,240 miles.
Clouded Yellow
The clouded yellow (Colias croceus) breeds in North Africa and the Middle East. Each spring, populations fly north to colonize central and northern Europe. Reverse migrations allow the species to overwinter in warmer climes. Roundtrip journeys can cover 3,100 miles.
Migration Strategies and Behaviors
Butterflies and moths use incredible sensory capabilities and energy-efficient flight to migrate huge distances. Some key behaviors and strategies include:
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Multigenerational migration – Journeys occur over successive breeding cycles. Each generation travels part of the route.
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Nocturnal migration – Many species migrate at night to avoid overheating and predation. Light from the moon and stars aids navigation.
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High-altitude migration – Flying at high elevations allows migrants to ride favorable winds over long distances.
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Resource tracking – Migratory populations closely follow seasonal changes in host plant availability across continents.
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Navigation – Butterflies and moths use the sun’s position, polarized light patterns, and Earth’s magnetic field to navigate during migration.
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Energy conservation – Special behaviors like flying in formation allow migrants to conserve energy on long flights.
Threats to Migratory Lepidoptera
Changing climate conditions and habitat loss along migratory pathways threaten many migratory butterflies and moths. Disruptions to breeding, feeding, and overwintering habitats can have catastrophic ripple effects on migratory populations.
Sustained research, habitat conservation, and citizen science monitoring will be key to protecting these insects and their incredible migratory abilities into the future. Their long-distance movements connect ecosystems across borders and continents. Losing migratory Lepidoptera would represent deep environmental losses around the globe.
Guide to Monarch Instars
Body Length: 2 to 6 mm Body width: 0.5 to 1.5 mm Front Tentacles: Small bumps Back tentacles: Barely visible Head Capsule: 0.6 mm in diameter
A newly-hatched monarch larva is pale green or grayish-white, shiny, and almost translucent. It has no stripes or other markings. The head looks black, with lighter spots around the antennae and below the mouthparts, and may be wider than the body. There is a pair of dark triangular patches between the head and front tentacles, which contain setae, or hairs. The body is covered with sparse setae. Older first-instar larvae have dark stripes on a greenish background. After hatching, the larva eats its eggshell (chorion). It then eats clusters of fine hairs on the bottom of the milkweed leaf before starting in on the leaf itself. It feeds in a circular motion, often leaving a characteristic, arc-shaped hole in the leaf. First (and second) instar larvae often respond to disturbance by dropping off the leaf on a silk thread and hanging suspended in the air. Time in this larval stage is usually 1-3 days, temperature dependent.
Body Length: 6 to 9 mm Body Width: 1 to 2 mm Front Tentacles: 0.3 mm Back Tentacles: Small knobs Head Capsule: 0.8 mm in diameter
Second-instar larvae have a clear pattern of black (or dark brown), yellow, and white bands, and the body no longer looks transparent and shiny. An excellent characteristic to use in distinguishing first and second instar larvae is a yellow triangle on the head and two sets of yellow bands around this central triangle. The triangular spots behind the head do not have the long setae present in the spots on the first instar larvae. The setae on the body are more abundant and look shorter and more stubble-like than those on first-instar larvae. Time in this larval stage is usually 1-3 days, temperature dependent.
3rd instar (Kristen Kuda)
Body Length: 10 to 14 mm Body Width: 2 to 3.5 mm Front Tentacles: 1.7 mm Back Tentacles: 0.9 mm Head Capsule: 1.5 mm in diameter
The black and yellow bands on the abdomen of a third instar larva are darker and more distinct than those of the second instar, but the bands on the thorax are still indistinct. The triangular patches behind the head are gone and have become thin lines that extend below the spiracle. The yellow triangle on the head is larger, and the yellow stripes are more visible. The first set of thoracic legs is smaller than the other two and is closer to the head. Time in this larval stage is usually 1-3 days, temperature dependent.
Third-instar larvae usually feed using a distinct cutting motion on leaf edges. Unlike first and second instar larvae, third (and later) instars respond to disturbance by dropping off the leaf and curling into a tight ball. Monarch biologist Fred Urquhart called this behavior “playing possum.”
4th instar (Kristen Kuda)
Body Length: 13 to 25 mm Body Width: 2.5 to 5 mm Front Tentacles: 5 mm Back Tentacles: 2 mm Head Capsule: 2.2 mm in diameter
Fourth-instar larvae have a distinct banding pattern on the thorax, which is not present in third instars. The first pair of legs is even closer to the head, and there are white spots on the prolegs that were less conspicuous in the third instar. Male and female larvae cant be distinguished by the naked eye until the pupal stage. However, male and female respective reproductive organs are visible in dissected, third, fourth, and fifth instars. Time in this larval stage is usually 1-3 days, temperature dependent.
5th instar (Kristen Kuda)
Body Length: 25 to 45 mm Body Width: 5 to 8 mm Front Tentacles: 11 mm Back Tentacles: 4 mm Head Capsule: 3.5 mm in diameter
The body pattern and colors of the fifth instar larvae are even more vivid than they were in the fourth instar, and the black bands look wider and almost velvety. The front legs look much smaller than the other two pairs and are even closer to the head. There are distinct white dots on the prolegs, and the body looks quite plump, especially just prior to pupating. Fifth-instar monarch larvae often chew a shallow notch in the petiole of the leaf they are eating, which causes the leaf to fall into a vertical position. They move much farther and faster than other instars and are often found far from milkweed plants as they seek a site for pupating. Time in this larval stage is usually 3-5 days, temperature dependent.
Just before they pupate, monarch larvae spin a silk mat from which they hang upside down by their last pair of prolegs. The silk comes from the spinneret on the bottom of the head. As it sheds its skin for the last time, the caterpillar stabs a stem into the silk pad to hang. This stem extends from its rear end and is called the cremaster.
While the process of complete metamorphosis looks like four very distinct stages, continuous changes actually occur within the larva. The wings and other adult organs develop from tiny clusters of cells already present in the larva, and by the time the larva pupates, the major changes to the adult form have already begun. During the pupal stage, this transformation is completed. Many moth caterpillars (but not all) spin a silken cocoon to protect them as pupae. Butterflies do not do this, and their pupa stage is often called a chrysalis. While it is fine to refer to the previous stage as either larva or caterpillar, it is not correct to call a butterfly pupa a cocoon since it does not have a silken covering.
Just before the monarchs emerge, their black, orange, and white wing patterns are visible through the pupa covering. This is not because the pupa becomes transparent; it is because the pigmentation on the scales only develops at the very end of the pupa stage. This stage of development lasts eight to fifteen days under normal summer conditions.
The primary job of the adult stage is to reproduce—to mate and lay the eggs that will become the next generation. Monarchs do not mate until they are three to eight days old. When they mate, they remain together from one afternoon until early the next morning—often up to 16 hours! Females begin laying eggs immediately after their first mating, and both sexes can mate several times during their lives. Adults in summer generations live from two to five weeks.
Each year, the final generation of monarchs, adults that emerge in late summer and early fall, has an additional job. They migrate to overwintering grounds, either in central Mexico for eastern monarchs or in California for western monarchs. Here they spend the winter clustered in trees until weather and temperature conditions allow them to return to their breeding grounds. These adults can live up to nine months.
Male and female monarchs can be distinguished easily. Males have a black spot on a vein on each hind wing that is not present on the female. These spots are made of specialized scales, which produce a chemical used during courtship in many species of butterflies and moths, although such a chemical does not seem to be important in monarch courtship. The ends of the abdomens are also shaped differently in males and females, and females often look darker than males and have wider veins on their wings.
Photos (left to right): female monarch abdomen, female monarch wings, male monarch abdomen, male monarch wings
The body of an adult butterfly is divided into the same major parts as the larva: head, thorax, and abdomen. There are four main structures on the adult head: eyes, antennae, palpi, and proboscis. A butterfly’s relatively enormous compound eyes are made up of thousands of ommatidia, each of which senses light and s. The two antennae and the two palpi, which are densely covered with scales, sense molecules in the air and give butterflies a sense of smell. The straw-like proboscis is the butterfly’s tongue, through which it sucks nectar and water for nourishment. When not in use, the butterfly curls up its proboscis.
Photos (left to right): monarch compound eyes (Michelle Solensky), adult tarsus (Michelle Solensky), monarch proboscis (Sonia Altizer), monarch wings scales (Michelle Solensky)
The thorax is made up of three segments, each of which has a pair of legs attached to it. The second and third segments also have a pair of wings attached to them. The legs end in tarsi (singular, tarsus), which grip vegetation and flowers when the butterfly lands on a plant. Organs on the back of the tarsi “taste” sweet liquids. Monarchs and other nymphalid butterflies look like they only have four legs because the two front legs are tiny and curl up next to the thorax.
Photos (left to right): Monarch aposematic coloration, Monarch nectaring, Monarch on coneflower
The monarchs that spend the winter in the mountains of central Mexico are the final generation of a cycle that begins anew each year. Most of the butterflies in this final generation begin their lives in the northern US or southern Canada and then migrate thousands of kilometers to mountaintops that neither they nor their parents (and likely their grandparents) have ever seen before. After spending several months in Mexico, they return north beginning in March, starting the cycle again as they lay eggs in northern Mexico and the southern US. Their parents, grandparents, and great-grandparents have very different lives. These summer monarchs live only about a month as adults and begin laying eggs when they are only a few days old.
In most years, the total number of monarchs probably increases with each generation. Because the winter generation must live for such a long time before reproducing, the entire population shrinks as some of these individuals die during the fall migration and overwintering period. The population then grows over the spring and summer.
| Generation # | Timing of immature stages* | Timing of adult stages* | Migrates? | Overwinter? |
| 1 | March-May | April-June | Yes, north in spring | No |
| 2 | May-July | June-July | North, through early June | No |
| 3 | July-August | July-August | Some movement south | Some |
| 4 | July-October | August-April | Yes, south in fall and north in spring | Yes |
*Months during which each generation exists.
Information on the monarch migration are taken from papers by S.B. Malcolm, B.J. Cockrell, and L.P. Brower and from data collected by the Journey North website.
Monarchs in Generation 1 are the offspring of the monarchs that overwinter. They are laid from late March through April in the southern United States and northern Mexico and fly north as adults. They do not undergo reproductive diapause.
The first monarch generation of the year begins when females who have spent the winter in Mexico lay eggs in northern Mexico and the southern U.S., beginning in late March. The last eggs are laid in late April or early May, farther north. Since it is often cool when Generation 1 larvae are developing, it may take them up to 40 or 50 days, or even more, to develop from eggs to adults.
Generation 1 adults emerge from late April to early June. They mate and begin to lay eggs about four days after emerging. They then continue the journey north that their parents began, laying eggs along the way. They begin to arrive in the northern US and southern Canada in late May.
Like all monarchs, this generation begins life on plants in the genus Asclepias (milkweeds). The most important host plants for Generation 1 monarchs in the southern US are Asclepias oenotheroides, Asclepias viridis, and Asclepias asperula.
Monarchs in Generation 2 are the grandchildren of the overwintering monarchs. They are laid throughout much of eastern North America from late April through June. They do not undergo reproductive diapause.
Generation 2 larvae are widely distributed throughout the eastern United States, first beginning to appear in the south in early May and in the north in mid to late May. Eggs that become generation 2 may be laid as late as July in the north. These larvae also eat milkweed species; a few of the main species that they use include A. syriaca (common milkweed), A. incarnata (swamp milkweed), and A. tuberosa (butterfly milkweed).
Generation 2 adults emerge in June and July and mate and lay eggs soon after emerging. Most of those who begin their lives in the south move north as adults since the southern summers are too hot and dry for their offspring. Those laid farther north probably do not move far and can use all of their energy to produce as many offspring as possible.
How We Finally Solved the Monarch Butterfly Migration Mystery
FAQ
Do butterflies and moths migrate?
Many populations of Lepidoptera (butterflies or moths) migrate, sometimes long distances, to and from areas which are only suitable for part of the year. Lepidopterans migrate on all continents except Antarctica, including from or within subtropical and tropical areas.
Where do moths and butterflies go in the winter?
Most butterflies and most other insects don’t migrate. Instead, they hide in the landscape in various stages of their life cycles for the winter months.Aug 30, 2022
What are migrating butterflies called?
Every year as it gets colder, North American monarch butterflies migrate south between August and October. Monarchs that spend the summer breeding west of the Rocky Mountains tend to migrate to California coasts, while monarchs breeding further east migrate to Mexico.
What months do butterflies migrate?
Mid-August typically marks the start of fall migration for millions of monarch butterflies. Adult monarchs are partway through their lifecycle, but their reproduction is on hold. These monarchs are different from their parents, grandparents and even great grandparents.