Danaus plexippus

The monarch is one of the best known butterfly species. Although native to North and South America, it has expanded its distribution to Australia, many Pacific islands, and a few places in Europe. Monarch larvae, like those of many other Danaini, feed on milkweeds of the family Asclepiadaceae, from which they sequester cardiac glycosides that often render them unpalatable to potential predators. The species is perhaps best known for its annual migrations, from eastern North America to the mountains of central Mexico, and from western North America to the coast of California. The butterflies rest for the cool winter months in large aggregations which may contain tens of millions of individuals.

Left: Monarch larva feeding on milkweed host plant at Poco Sol (Caribbean slope below Monteverde), Costa Rica. Right: Overwintering monarchs covering a tree branch at Alpha Monarch research site, Mexico. Images © Greg and Marybeth Dimijian

Danaus plexippus is a year-round resident in Calif. and s. Fla. and migratory through most of North America (Scott 1986). The eastern population exhibits a fantastic and unique migratory habit, with adults overwintering in a small forest are in central Mexico and spring migrants laying eggs and expanding over several generations until they reach Canada in late summer. California populations overwinter in forest stands along the coast and migrate inward. Populations in south Florida do not migrate. Breeding habitats are mostly open places, esp. moist valley bottoms, breeding from the subtropics to the lower Canadian zone. Host plants are herbaceous and include many species but restricted mostly to family Asclepiadaceae. Eggs are laid on the host plant singly. Individuals overwinter as adults, by roosting in trees. There are five or more flights all year in Calif. and s. Fla.; in New Mexico and s. Nev. several flights Mar.10-Nov.30; in the northeast May1-Oct31; in Nfld, Aug1-Oct.31. (Scott 1986).

The black-veined, orange upperside with a white-spotted black border is unique. The Viceroy (Limenitis archippus) though similar, has a black hindwing median line. Monarchs are easy to recognize by their distinctive leisurely, floating flight, holding their wings V-shaped above the body when gliding; Viceroys hold their wings in a flat plane when gliding, a behaviour characteristic of the genus Limenitis.

Monarch butterflies are found in North America, South America, the Caribbean, Australia, New Zealand, islands in the Pacific Ocean, Mauritius, the Canary Islands of the Atlantic, and Western Europe.

Globally widespread, with the centre of the range in North America from BC east to Newfoundland, north to the southern NWT south to Argentina (Layberry et al 1998).

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) The Monarch butterfly is attaining near worldwide distribution in suitable places, but is primarily a species of the Americas. Autumnal migrants occasionally stray to Europe including England; the species has been spread widely in the Pacific Ocean area and is well-established in Australia. However, the seasonal ranges in North America are vastly different, by millions of square kilometers. Essential overwintering areas for North American populations are limited to a few dozen places in coastal California and the mountains of Mexico. Specifically that means that the summer range includes portions of up to 49 of the 50 US states and southern portions of all Canadian Provinces bordering the US where milkweeds occur. However the winter range includes none of Canada and in the US only a few dozen square kilometers in California, and at least some years a bit of south Florida. Florida winter populations may be non-migratory and if so contribut little to summer populations. Some winters a few may persist in sothern Arizona.

Both male and female monarchs are bright orange with black borders and black veins. The veins on the female are thicker than those of the male. Male monarchs also have a swollen pouch on both of their hind wings.

Monarchs are poisonous to vertebrates. Their poison comes from the milkweed they feed on.

Monarchs also use their appearance to ward off predators. Orange is considered a warning color, which will warn predators that monarchs are poisonous, and not to attack them. From a distance, monarchs can blend into their surroundings. Sometimes, their spots will appear to be the eyes of a larger animal, and will ward off predators.

Range wingspan: 8.6 to 12.4 cm.

Other Physical Features: ectothermic ; bilateral symmetry ; poisonous

Monarch butterflies have a wingspan of 3-4 1/2 inches (75-114 mm). The male is bright orange and has a black scent patch in the middle of the upper hind wing. The female is dull orange or brown with more thickly scaled black veins. The underside of the hind wing is light orange with black veins and a marginal black border with two rows of white spots. The upper front wing has a black apex (tip) with white spots. The sub-apex has light orange spots on a dark background. The underside of the front wing has white spots and yellow ovals in the outer portion.

Monarch butterflies prefer warmer climates; they cannot tolerate frost. They like open country. Females spend much of their time around searching for or staying near the main food plant for the caterpillars (see food habits section). Monarch butterflies require thick tree covering during the winter. In California, they live in eucalyptus trees. These eucalyptus trees are not normally found in California, but were put there to replace trees that had been cut down.  Biomes: temperate forest and rainforest, temperate grassland, chaparral, tropical rainforest, tropical deciduous forest, tropical scrub forest, tropical savanna and grasslands, mountains

Comments: Habitat is a complex issue for this species. In general breeding areas are virtually all patches of milkweed in North America and some other regions. The critical conservation feature for North American populations is the overwintering habitats, which are certain high altitude Mexican conifer forests or coastal California conifer or Eucalyptus groves as identified in literature. It appears virtually all North American monarchs overwinter in one of these two areas. Lethal cold would preclude successful overwintering in places like the Gulf Coast and much of Florida some years and it appears thse are not major wintering regions as used to be assumed. In addition certain major coastal migratory stopovers may be important conservation sites especially those in along Delaware Bay in New Jersey including Cape May where adults may holdover for several days awaiting suitable conditions for crossing the Bay. There are major, but probably less important, roosting sites farther north such as east of New Haven and probably others farther south perhaps even as far as Cuba. Coastal regions are important flyways and so nectar (wild or in gardens) is an important reseource in such places. In places like Hawaii and some others the species simply breeds year round and is not really migratory.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Monarch females lay their eggs on milkweed plants (Asclepias), these plants are then the main food for the caterpillars. Adult monarchs feed on nectar from many kinds of flowers.

The main larval host in Alberta is Showy Milkweed (Asclepias speciosa), and larvae have also been recorded on A. ovalifolia in Edmonton (Bird et al. 1995). Adults prefer nectaring at milkweed flowers and composites (Klassen et al. 1989).

Comments: Larval foodplants are milkweeds.

Danaus plexippus Linnaeus: Nymphalidae, Lepidoptera
(observations are from Robertson, Graenicher, Betz et al., Reed, Hilty, Clinebell, Smith & Snow, Hapeman, Macior, Broyles & Wyatt, Willson & Bertin, Fothergill & Vaughn; this is the Monarch butterfly)

Apiaceae: Eryngium yuccifolium sn (Rb), Pastinaca sativa sn (Rb), Sium suave sn (Rb), Torilis arvensis sn (FV); Asclepiadaceae: Ampelamus albidus [plup sn] (H), Asclepias exaltata [plup sn] (BW), Asclepias incarnata [plpr sn] [plup sn] (Rb, Btz), Asclepias syriaca [plpr sn] (Rb), Asclepias tuberosa [plab] [plup] (Rb, Btz, H), Asclepias verticillata [plpr sn] [plup sn] (Rb, WB); Asteraceae: Aster drummondii sn (Gr), Aster furcatus sn (Gr), Aster laevis sn (Gr), Aster lanceolatus sn (Gr), Aster macrophyllus sn (Gr), Aster novae-angliae sn (Rb, Gr, H), Aster pilosus sn (Rb), Aster puniceus sn (Gr), Aster salicifolius sn (Rb), Bidens aristosa sn (Rb), Bidens cernua sn fq (Rb), Boltonia asterioides sn (Rb), Cirsium altissimum sn (Gr), Cirsium discolor sn (Rb, H), Cirsium hillii sn (Rb), Cirsium vulgare sn (Rb, Gr), Conoclinium coelestinum sn (Rb), Coreopsis tripteris sn (Rb), Echinacea pallida sn (Rb), Echinacea purpurea sn (Rb, H), Eupatoriadelphus purpureus sn (Rb, Gr, H), Eupatorium altissimum sn (H), Eupatorium perfoliatum sn (Rb, Gr), Euthamia graminifolia sn (Gr), Helianthus annuus sn (Rb, H), Helianthus grosseserratus sn fq (Rb), Helianthus mollis sn (H), Helianthus strumosus sn (Gr), Heliopsis helianthoides sn (Gr), Liatris aspera sn (Rb, H), Liatris pycnostachya sn (Rb), Liatris spicata sn (Gr), Oligoneuron rigidum sn (H, Re), Rudbeckia laciniata sn (Gr), Silphium integrifolium sn (H), Silphium laciniatum sn (Rb), Silphium perfoliatum sn (Rb), Silphium terebinthinaceum sn (H), Solidago canadensis sn (Rb, Gr), Solidago nemoralis sn (Rb), Taraxacum officinale sn (FV), Vernonia fasciculata sn (Rb); Boraginaceae: Mertensia virginica sn (Rb); Campanulaceae: Lobelia siphilitica sn (Rb); Caprifoliaceae: Symphoricarpos albus sn (Gr), Symphoricarpos occidentalis sn (Gr); Dipsacaceae: Dipsacus fullonum sn (Rb); Fabaceae: Melilotus alba sn (Rb), Robinia pseudoacacia sn np (Rb), Trifolium pratense sn (Rb), Trfiolium repens sn (FV); Lamiaceae: Agastache nepetoides sn (Rb), Blephilia hirsuta sn (Rb), Monarda fistulosa sn (Rb, Cl), Physostegia virginiana sn np (Rb), Salvia azurea sn np (H); Liliaceae: Lilium michiganense sn (Rb); Orchidaceae: Platanthera blephariglottis sn (SS), Platanthera ciliaris sn (SS), Platanthera peramoena sn (Hpm); Polemoniaceae: Phlox divaricata laphamii sn (Rb), Phlox glaberrima sn (Rb); Polygonaceae: Persicaria pensylvanica sn (H); Ranunculaceae: Delphinium tricorne sn np (Rb, Mc); Rosaceae: Crataegus crus-galli sn (Rb), Crataegus intricata sn (Rb), Malus coronaria sn (Rb), Prunus americana sn (Rb), Prunus serotina [flwr sn] (Rb); Rubiaceae: Cephalanthus occidentalis sn fq (Rb); Verbenaceae: Verbena stricta sn (Rb); Violaceae: Viola sororia sn (FV)

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

Comments: This refers to global occurrences for the species as a whole and includes introduced populations in Hawaii, Australia etc., as well as central and South America. In these places and where non-migratory native populations occur, habitat may be more or less used all year. North American populations also have a lot of breeding habitat, most of it patchy and suboptimally managed for Monarch survival, but still producing millions of adults each summer. These face an annual bottleneck in terms of dependence on a few dozen overwintering areas. Western North American populations may also be under pressure from scarcity of good breeding sites, especially in dry years, and incompatible management.

>1,000,000 individuals

Comments: At least millions of individuals, probably more than a billion in many years, worldwide.

Can contain poison derived from their larval foodplant that helps avoid predation by birds (Scott, 1986).

Adults feed mainly on flower nectar. Males patrol for females (Scott, 1986).

Migrants reach southern Alberta in late May to June, offspring emerging in Aug. to Sep.

Small caterpillars hatch from eggs laid by female Monarchs. They grow, shedding their skin to get bigger. Eventually each caterpillar stops growing and forms a case around itself called a chrysalis. Inside the chrysalis it changes its body its body in a process called metamorphosis. When it is done it emerges as an adult butterfly.

Development - Life Cycle: metamorphosis

Migrants from the southern US appear in the spring, and lay eggs on a number of milkweed species, particularly along prairie river valleys. Larvae are like no other in Alberta, boldly banded with alternating black, white and yellow stripes. There are two long, black fleshy 'horns' near the front and rear. Pupae are bright blue-green with golden spots. This is undoubtedly one of the most familiar butterflies in North America, and much research has been carried out on its ecology and remarkble migration. Surprisingly, the Monarch's wintering grounds in Mexico were not discovered until 1975, largely as a result of the research efforts of Fred Urquhart (Layberry et al. 1998). Almost all of the North American Monarchs overwinter in a handful of sites in the Mexican highlands, and conservation efforts for this species are largely dependent on the welfare of these sites. For more detailed accounts of the Monarch's ecology, see Brower (1995) and references therein.

The mating period occurs in the spring, just prior to migration from the overwintering sites. The courtship of Danaus plexippus is fairly simple and less dependent on chemical pheromones in comparison with other species in its genus. Courtship is composed of two distinct stages, the aerial phase and the ground phase. During the aerial phase, the male pursues, nudges, and eventually takes down the female. Copulation occurs during the ground phase and involves the transfer of a spermatophore from the male to female. Along with sperm, the spermatophore is thought to provide the female with energy resources that aid her in carrying out reproduction and remigration.

Breeding interval: Monarch butterflies mate in the spring before they migrate.

Key Reproductive Features: semelparous ; sexual ; fertilization (Internal ); oviparous

In Baja California may be encountered throughout the year (November-April in coastal regions and June-October in the Mountains) (Brown et al., 1992)

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 18
Specimens with Barcodes: 82
Species With Barcodes: 1

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 39 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

Download FASTA File

The places where monarchs spend the winter are threatened. The United States and Mexico are trying to help the areas where monarch butterflies migrate.

IUCN Red List of Threatened Species: no special status

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

The Monarch is of special concern in Canada (COSEWIC 2002).

Rounded Global Status Rank: G5 - Secure

Reasons: The Monarch is globally secure, because it is doing well in many places where populations are not native and/or not strongly migratory, which drives the G5 rank. However, this is misleading in North America where the Monarch is no longer secure because of serious threats to their obligate overwintering areas in Mexico (mostly) and and a recent order of magnitude decline in California based population, which apparently reflects threats in the western breeding range. Threats also exist in the eastern spring migration route (especially in Texas). The migratory North American populations have been declining in recent years with 2009 among the worst ever (2010 data not evaluated) for California winter population. Deteriorating spring climate conditions in Texas appear to be a major contributor to recently declining numbers in the eastern US in the 2000s. Western North American populations are probably more threatened than eastern ones because suitable milkweeds are less reliable in generally more arid western regions in dry periods. Rank Calculator v3.0 is also G5. Regardless of the fate of North american populations, the species as a whole is globally secure.

Environmental Specificity: Broad. Generalist or community with all key requirements common.

Comments: Very broad as a breeder everywhere and globally overall, but very narrow for overwintering populations in North America.

Other Considerations: Elimination of Mexican sites would mean virtual extinction of eastern North American populations. Nearly all western individuals had been thought to winter in California, but some of these also go to th mountains of Mexico. This species has become a significant ecotourism resource locally in Mexico.

Canada

Rounded National Status Rank: N4B - Apparently Secure

United States

Rounded National Status Rank: N5B,N2N : N5B: Secure - Breeding, N2N: Imperiled - Nonbreeding

Global Short Term Trend: Increase of 10-25% to decline of 30%

Comments: Difficult to assess globally. Stable to increasing in many places where it is not native and in some Neotropical places where it is. North American populations, which are still a large portion of the global total, are well documented to be declining, but fluctuate from year to year. California based populations may be down more than 90% from 1997-2009.

Global Long Term Trend: Increase of >25% to decline of 50%

Comments: See short term.

Degree of Threat: Medium

Comments: The species as a whole is not seriously threatened, but the typical subspecies may be secure mostly where it is not native. The monarch appears to be doing well or even increasing in may places, but not in its core North American range. The native eastern North American populations are in trouble at their overwintering grounds. Overwintering habitats in Mexico are primarily in a few hectares each and have been under pressure from logging, agricultural and urban development. California based populations are declining more due to problems in the breeding areas. Climate change is emerging as a current, rather than an expected, threat in Mexico, California, and Texas at least. There was some improvement in the eastern, as well as western, USA in 2010 so at least populations can still respond quickly to temporarily good conditions. Regardless of what happens in North America this species is at virtually no risk of global extinction in the forseeable future.

Biological Research Needs: The basics of Monarch biology, migration, etc. are now rather well known, although some of the details regarding western US populations may still need resolution. Main needs now appear to be understanding impacts of and how to prevent or mitigate habitat changes and climate change primarily in overwintering areas and during spring migration particularly in Texas. Accurate information for Central and South America needs to be compiled, because this is globally significant to the species even if unrelated to its status in North America.

Global Protection: Unknown whether any occurrences are appropriately protected and managed

Comments: Too difficult to assess because needs vary so widely with local ecology.

Needs: Winter habitats in California and Mexico need protection from logging, development, etc. This need has been known for decades. In the near term mitigation of climate change impacts could become an urgent need.

Some milkweed plants are poisonous to cattle. Monarch butterflies help reduce the amount of these plants.

Compared to bees, butterflies are often less efficient at transferring pollen between plants because pollen often does not stick to their bodies and they lack specialized structures for collecting pollen. However, on the occasions in which pollen does stick to the butterflies' bodies, it is often inadvertently transferred to another flower while the butterflies are nectaring, earning them the title of pollinators.

Research has shown that most butterfly species do indeed end up pollinating some of the flowers they visit, and because monarch butterflies have such a long migration route they are potential pollinators to plants across the country! Studies have found that monarch butterflies do carry pollen from swamp milkweed (Asclepias incarnata) and are, therefore, potential pollinators. Monarch butterflies are known pollinators of common milkweed (Asclepias syriaca), butterfly weed (Asclepias tuberosa), and rattlesnake master (Eryngium yuccifolium). Additionally, monarch butterflies feed on the nectar of many other plants, like rabbitbrush (Ericameria nauseosa), desert broom (Baccharis spp.), aster (Aster spp.), sunflower (Helianthus spp.), goldenrod (Solidago spp.), verbena (Verbena spp.), clover (Trifolium spp.), and other milkweed species (Asclepias spp.).

Although adult monarchs feed on the nectar of many flowers, they will breed only where milkweed plants are found. That is because monarch larvae feed exclusively on milkweed plants. Milkweed plants contain compounds called cardenolide alkaloids that are toxic to most vertebrate herbivores if ingested. However, while monarch larvae feed on milkweed plants they also ingest the toxins. They then sequester the compounds in their bodies, wings, and exoskeletons, making both the larvae and adult butterflies toxic to many predators.