Monarchs are well-known butterflies distinguished by their relatively large size, rusty or orange wings with black veins, and black bodies. The upper surfaces of the wings are rusty or tawny orange with black veins; the wing edges are black with small white spots. The undersides of wings are lighter orange or yellow-brown. The veins are darker on females, and males have a black spot on their hindwings.
The caterpillars are white with black and yellow bands; the head is white with yellow and black markings; a pair of long, black filaments are on the thorax and a shorter pair near the end of the abdomen. The caterpillars are usually are found on milkweeds.
Wingspan: 3½–4 inches; larvae can grow up to 2 inches long.
Habitat and Conservation
In Missouri, monarchs are found in a wide variety of habitats: fields and grasslands, roadsides, and urban and suburban plantings. They are famous for their annual migration to overwinter in Mexico.
A variety of factors are causing the numbers of this iconic species to decline. Habitat loss in their overwintering territory in Mexico is one cause. Also, herbicide use throughout North America has been eliminating milkweeds, their required larval food plant, as well as eliminating the once-common scrubby fencerows and other tracts of various wildflowers adults need for nectar. Especially in the Midwest, herbicide-resistant strains of crops allow farmers to eradicate nearly all non-crop herbaceous plants, including milkweeds, across vast areas, eliminating places for the monarch to breed and feed. To conserve the monarch, we must allow milkweeds to grow.
Missourians are encouraged to plant milkweeds for the larvae and a variety of native wildflowers that supply nectar throughout the entire growing season for the adults.
Monarch larvae feed on a variety of milkweeds, which contain cardiac glycosides. These chemicals are stored in the insect’s body and render it unpalatable and toxic to many predators. The bright color patterns of both larvae and adults advertise their toxicity to would-be predators.
As adults, monarchs consume the nectar of a wide variety of flowers, particularly New England aster and other members of the sunflower family.
Declining throughout North America and may soon have federal protected status.
On July 21, 2022, the International Union for Conservation of Nature (IUCN) placed the migratory monarch (subspecies D. p. plexippus) on the IUCN Red List of Threatened Species, listing it as endangered, and noting that its primary threats are habitat destruction and climate change. The IUCN is an international group of government and civil society organizations headquartered in Switzerland. Announcing the decision, the IUCN noted that the migratory monarch, "known for its migrations from Mexico and California in the winter to summer breeding grounds throughout the United States and Canada, has shrunk by between 22% and 72% over the past decade. Legal and illegal logging and deforestation to make space for agriculture and urban development has already destroyed substantial areas of the butterflies’ winter shelter in Mexico and California, while pesticides and herbicides used in intensive agriculture across the range kill butterflies and milkweed, the host plant that the larvae of the monarch butterfly feed on."
In its announcement, the IUCN continued: "Climate change has significantly impacted the migratory monarch butterfly and is a fast-growing threat; drought limits the growth of milkweed and increases the frequency of catastrophic wildfires, temperature extremes trigger earlier migrations before milkweed is available, while severe weather has killed millions of butterflies." The IUCN noted that eastern and western populations are both in trouble. "The western population is at greatest risk of extinction, having declined by an estimated 99.9%, from as many as 10 million to 1,914 butterflies between the 1980s and 2021. The larger eastern population also shrunk by 84% from 1996 to 2014. Concern remains as to whether enough butterflies survive to maintain the populations and prevent extinction."
Broods are produced in Missouri in summer and fall. Adults migrate to Mexico in late summer and fall; then, when they fly north in spring, they reproduce in Oklahoma or Texas. Their offspring continue northward, returning “home” some generations later. Eggs are laid in the spring and summer and hatch in about 4 days. The caterpillars eat milkweed. After about 2 weeks, the caterpillar enters the chrysalis stage. The mature butterfly emerges in about 2 weeks.
Monarchs, beautiful and delicate creatures, are capable of making miraculous journeys as they migrate. Everyone can do something to help them. Anna Walker, a member of the IUCN who led the monarch butterfly assessment, had encouraging words: "It is difficult to watch monarch butterflies and their extraordinary migration teeter on the edge of collapse, but there are signs of hope. So many people and organisations have come together to try and protect this butterfly and its habitats. From planting native milkweed and reducing pesticide use to supporting the protection of overwintering sites and contributing to community science, we all have a role to play in making sure this iconic insect makes a full recovery."
Monarchs are extremely popular with gardeners and nature watchers. Artists and graphic designers commonly depict monarchs on things like decorative flags, pillows for outdoor furniture, and garden smocks.
Educators commonly raise monarchs as a way of teaching about insect life cycles.
Where they flock in great numbers, monarchs can contribute to the local tourism economy.
Monarchs play an important role in all the ecosystems they pass through during migration. Despite the monarchs’ general toxicity, some predators, such as spiders and mantids, can eat them. In this way, they function as other herbivorous insects that pass nutrients upward to predators through the food chain.
Monarchs are part of an intricate color-signal system affecting the fortunes of a variety of insects. With their distinctive coloration and icky flavor or sickening chemicals, they teach predators to avoid them, and anything that looks like them. There are several other insects with very similar color patterns. These include some close relatives of the monarch as well as the less-related viceroy butterfly; these are also distasteful to predators, and a predator being sickened by any member of this group reinforces the warning signal. When a group of insects display the same, truthful, warning signal coloration, they are called Müllerian mimics.