Appearance
Commonly and easily mistaken for the similar viceroy butterfly – the two species are Müllerian mimics, the monarch's wingspan ranges from 8.9 to 10.2 centimetres.The uppersides of the wings are tawny orange, the veins and margins are black, and there are two series of small white spots in the margins. Monarch forewings also have a few orange spots near their tips. Wing undersides are similar, but the tips of forewings and hindwings are yellow brown instead of tawny orange and the white spots are larger.
The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants. Wings size and shape differ between migratory and non-migratory monarchs. Monarchs from eastern North America have larger and more angular forewings than those in the western population.
Monarch flight has been described as "slow and sailing". Monarch flight speed has been estimated by a number of researchers. One scientist examined all prior estimates and concluded their flight speed is approximately 9 km/h or 5.5 mph. For comparison, the average human jogs at a rate of 9.7–12.9 km/h.
Adults are sexually dimorphic. Males are slightly larger than females and have a black patch or spot of androconial scales on each hindwing. The male's black wing veins are lighter and narrower than those of females.
One variation, the "white monarch", observed in Australia, New Zealand, Indonesia and the United States, is called "nivosus" by lepidopterists. It is grayish white in all areas of its wings that are normally orange and is only about 1% or less of all monarchs, but populations as high as 10% exist on Oahu in Hawaii.
The monarch has six legs like all insects, but uses only its middle legs and hindlegs as the forelegs are vestigial, as in all Nymphalidae, and held against its body.
Distribution
In the Americas, the monarch ranges from southern Canada through northern South America. It has also been found in Bermuda, Cook Islands, Hawaii, Cuba, and other Caribbean islands: the Solomons, New Caledonia, New Zealand, Papua New Guinea, Australia, the Azores, the Canary Islands, Madeira, Gibraltar, the Philippines, and North Africa. It appears in the UK in some years as an accidental migrant.Overwintering populations of "D. plexippus plexippus" are found in Mexico, California, along the Gulf Coast, year round in Florida, and in Arizona where the habitat has the specific conditions necessary for their survival.
On the US East Coast, they have overwintered as far north as Lago Mar, Virginia Beach, Virginia. Their wintering habitat typically provides access to streams, plenty of sunlight, and appropriate roosting vegetation, and is relatively free of predators.
Overwintering, roosting butterflies have been seen on basswoods, elms, sumacs, locusts, oaks, osage-oranges, mulberries, pecans, willows, cottonwoods, and mesquites. While breeding, monarch habitats can be found in agricultural fields, pasture land, prairie remnants, urban and suburban residential areas, gardens, trees, and roadsides – anywhere where there is access to larval host plants.
Habitat restoration is a primary goal in monarch conservation efforts. Habitat requirements change during migration. During the fall migration, butterflies must have access to nectar-producing plants. During the spring migration, butterflies must have access to larval food plants and nectar plants.
Status
The monarch butterfly is not currently listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora or protected specifically under U.S. domestic laws. On 14 August 2014, the Center for Biological Diversity and the Center for Food Safety filed a legal petition requesting Endangered Species Act protection for the monarch and its habitat, based largely on the long-term trends observed at overwintering sites.The U.S. Fish and Wildlife Service initiated a status review of the monarch butterfly under the Endangered Species Act with a due date for information submission of 3 March 2015. The decision on whether to list the monarch is still pending, and a new deadline for completion of an internal FWS species status report is December 2020.
Behavior
The monarch butterfly undergoes four stages of complete metamorphosis:
Reproduction
The eggs are derived from materials ingested as a larva and from the spermatophores received from males during mating. Eggs are laid singly on the underside of a young leaf of a milkweed plant during the spring and summer months.The eggs are cream colored or light green, ovate to conical in shape, and about 1.2×0.9 mm in size. The eggs weigh less than 0.5 mg each and have raised ridges that form longitudinally from the point to apex to the base. Though each egg is 1⁄1000 the mass of the female, she may lay up to her own mass in eggs.
Females lay smaller eggs as they age. Larger females lay larger eggs. The number of eggs laid by a female, who may mate several times, ranges from 290 to 1180. Females lay their eggs on the underside of the milkweed leaves; the offspring's consumption of the milkweed benefits health and helps defend them against predators.
Eggs take 3 to 8 days to develop and hatch into larva or caterpillars.: Monarchs will lay eggs along the southern migration route.The caterpillar goes through five major, distinct stages of growth and after each one, it molts. Each caterpillar, or instar, that molts is larger than the previous as it eats and stores energy in the form of fat and nutrients to carry it through the nonfeeding pupal stage. Each instar usually lasts about 3 to 5 days, depending on various factors such as temperature and food availability.
The first instar caterpillar that emerges out of the egg is pale green and translucent. It lacks banding coloration or tentacles. The larvae or caterpillar eats its egg case and begins to feed on milkweed. It is during this stage of growth that the caterpillar begins to sequester cardenolides. The circular motion a caterpillar uses while eating milkweed prevents the flow of latex that could entrap it. The first instar is usually between 2 and 6S mm long.
The second instar larva develops a characteristic pattern of white, yellow and black transverse bands. It is no longer translucent but is covered in short setae. Pairs of black tentacles begin to grow. One pair grows on the thorax and another pair on the abdomen. Like the first instar, second instar larvae usually eat holes in the middle of the leaf, rather than at the edges. The second instar is usually between 6 mm and 1 cm long.
The third instar larva has more distinct bands and the two pairs of tentacles become longer. Legs on the thorax differentiate into a smaller pair near the head and larger pairs further back. These third-stage caterpillars begin to eat along the leaf edges. The third instar is usually between 1 and 1.5 cm long.
The fourth instar has a different banding pattern. It develops white spots on the prolegs near the back of the caterpillar. It is usually between 1.5 and 2.5 cm long.
The fifth instar larva has a more complex banding pattern and white dots on the prolegs, with front legs that are small and very close to the head. A caterpillar at this stage has an enormous appetite, being able to consume a large milkweed leaf in a day. Its length ranges from 2.5 to 4.5 cm.
At this stage of development, it is relatively large compared to the earlier instars. The caterpillar completes its growth. At this point, it is 4.5 cm long and 7 to 8 mm wide, and weighs about 1.5 grams. This can be compared to the first instar, which was 2 to 6 mm long and 0.5 to 1.5 mm wide.
Fifth-instar larvae increase in weight 2000 times from first instars. Fifth-stage instar larva can chew through the petiole or midrib of milkweed leaves and stop the flow of latex. After this, they eat more leaf tissue.
Before pupation, larvae must consume milkweed to increase their mass. Larvae stop feeding and search for a pupation site. Healthy males are more likely to mate than unhealthy ones. Females and males typically mate more than once. Females that mate several times lay more eggs.
Mating for the overwintering populations occurs in the spring, prior to dispersion. Mating is less dependent on pheromones than other species in its genus. Male search and capture strategies may influence copulatory success, and human-induced changes to the habitat can influence monarch mating activity at overwintering sites.
Courtship occurs in two phases. During the aerial phase, a male pursues and often forces a female to the ground. During the ground phase, the butterflies copulate and remain attached for about 30 to 60 minutes.
Only 30% of mating attempts end in copulation, suggesting that females may be able to avoid mating, though some have more success than others. During copulation, a male transfers his spermatophore to a female. Along with sperm, the spermatophore provides a female with nutrition, which aids her in egg laying.
An increase in spermatophore size increases the fecundity of female monarchs. Males that produce larger spermatophores also fertilize more females' eggs.The host plants used by the monarch caterpillar include:
⤷ "Asclepias angustifolia" – Arizona milkweed
⤷ "Asclepias asperula" – antelope horns milkweed
⤷ "Asclepias californica" – California milkweed
⤷ "Asclepias cordifolia" – heartleaf milkweed
⤷ "Asclepias curassavica"
⤷ "Asclepias eriocarpa" – woolly pod milkweed
⤷ "Asclepias erosa" – desert milkweed
⤷ "Asclepias exaltata" – poke milkweed
⤷ "Asclepias fascicularis" – Mexican whorled milkweed
⤷ "Asclepias humistrata" – sandhill/pinewoods milkweed
⤷ "Asclepias incarnata" – swamp milkweed
⤷ "Asclepias nivea" – Caribbean milkweed
⤷ "Asclepias oenotheroide" – zizotes milkweed
⤷ "Asclepias perennis" – aquatic milkweed
⤷ "Asclepias speciosa" – showy milkweed
⤷ "Asclepias subulata" – rush milkweed
⤷ "Asclepias syriaca" – common milkweed
⤷ "Asclepias tuberosa" – butterfly weed
⤷ "Asclepias variegata" – white milkweed
⤷ "Asclepias verticillata" – whorled milkweed
⤷ "Asclepias vestita" – woolly milkweed
⤷ "Asclepias viridis" – green antelopehorn milkweed
⤷ "Calotropis gigantea" – crown flower
⤷ "Calotropis procera"
⤷ "Cynanchum laeve" – sand vine milkweed
⤷ "Sarcostemma clausa" – white vine
Food
Although larvae eat only milkweed, adult monarchs feed on the nectar of many plants including:⤷ "Apocynum cannabinum" – Indian hemp
⤷ "Asclepias" sp. – milkweeds
⤷ "Aster" sp. – asters
⤷ "Cirsium" sp. – thistles
⤷ "Daucus carota" – wild carrot
⤷ "Dipsacus sylvestris" – teasel
⤷ "Echinacea" sp. – coneflowers
⤷ "Erigeron canadensis" – horseweed
⤷ "Eupatorium maculatum" – spotted Joe-Pye weed
⤷ "Eupatorium perfoliatum" – common boneset
⤷ "Hesperis matronalis" – dame's rocket
⤷ "Liatris" sp. – blazing stars
⤷ "Medicago sativa" – alfalfa
⤷ "Solidago" sp. – goldenrod
⤷ "Syringa vulgaris" – lilac
⤷ "Trifolium pratense" – red clover
⤷ "Vernonia altissima" – tall ironweed
Monarchs obtain moisture and minerals from damp soil and wet gravel, a behavior known as mud-puddling. The monarch has also been noticed puddling at an oil stain on pavement.
Defense
In both caterpillar and butterfly form, monarchs are aposematic—warding off predators with a bright display of contrasting colors to warn potential predators of their undesirable taste and poisonous characteristics.Large larvae are able to avoid wasp predation by dropping from the plant or by jerking their bodies.
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