Monarch Butterfly

Quick Take

• A monarch's entire migratory ability, which spans thousands of miles, traces back to a single gene, and some populations have quietly switched it off.
• Monarchs are toxic to most predators, yet certain birds have cracked the code on how to eat them safely anyway.
• The last generation of monarchs born each season lives dramatically longer than every generation before it, a fact whose explanation changes everything about how their migration works.
• Nearly a billion monarchs have vanished from their overwintering sites, yet they still aren't classified as endangered. The reason why turns out to be surprisingly complicated.

Monarch butterflies are known for their very distinct orange, black, and white coloring. These amazing creatures go through four stages in their life cycle: egg, larva, pupa, and adult. While some adult monarch butterflies may only live for two to six weeks, during migration they can live for eight or nine months. When they migrate in the fall, a monarch butterfly will travel thousands of miles. While they fly on their own during the day, they will form large groups, known as roosts, at night.

Incredible Monarch Butterfly Facts

• The four stages in the life cycle of a monarch butterfly are egg, larva, pupa, and adult.
• Monarchs have black, orange, and white coloring, which makes them easy to identify.
• During migration, monarchs may fly thousands of miles.
• Losing their habitats is one of the biggest threats faced by monarchs.
• Female monarchs lay their eggs on milkweed plants.

Evolution

Monarchs have developed a wide array of evolutionarily beneficial traits throughout the course of their existence. Scientists believe that monarchs originated in North and South America and migrated elsewhere some time thousands of years ago. Recent genetic studies have revealed that the monarch’s complex migratory abilities involve a sophisticated genetic architecture spanning multiple genes and epigenetic factors, such that populations that once migrated great distances across vast oceans to arrive in new habitats stopped expressing these traits once they had settled.

Monarchs have also developed a resistance to toxic plants that they ingest to fend off predators. This is the reason why monarchs are considered poisonous, though the amounts of toxin present in their bodies are not high enough to harm humans or do significant damage to animals like cats and dogs.

Scientific Names and Types of Monarchs

Monarch butterflies are in the class Insecta and belong to the family Nymphalidae. Their scientific name is Danaus plexippus. Danaus refers to a genus of butterflies, and plexippus refers to the specific monarch butterfly species.

Monarch butterflies are divided into 6 subspecies:

• Danaus plexippus plexippus: It is the iconic long-distance migratory monarch found across North America (southern Canada down to Mexico).
• Danaus plexippus megalippe: A non-migratory subspecies found in parts of the southern United States (such as Florida and Georgia southward), as well as Central America, the Caribbean, and northern South America.
• Danaus plexippus portoricensis: A localized subspecies native to Puerto Rico.
• Danaus plexippus leucogyne: A subspecies native to the Virgin Islands.
• Danaus plexippus tobagi: A subspecies described from the island of Tobago.
• Danaus plexippus nigrippus: A subspecies described from parts of South America.

Appearance and Behavior

Monarch butterflies have a very distinct appearance, which makes them easy to identify. The top portion of their wings is orange with black veins, numerous white spots around the perimeter of the wings, and a few orange spots near the tips of the wings. The underside of a monarch butterfly’s wings looks similar to the upper side. However, instead of being a bright orange color, the wings are more of a yellow-brown color. The white spots on the undersides of their wings are larger than the ones found on the upper sides.

Throughout the migration season, the wings of different monarch butterflies may have a different appearance. Toward the beginning of the migration, a monarch’s wings appear longer and redder than those of monarchs migrating later in the season. Additionally, the wings of monarchs that migrate differ slightly from those that do not.

A monarch butterfly’s wingspan is between 3 and 4 inches wide; this is as wide as or a little wider than the average width of an adult male’s hand.

California tortoiseshell butterflies, painted lady butterflies, western tiger swallowtail butterflies, viceroy butterflies, and queen butterflies all may be confused for monarchs because of their similar coloring. All of these butterflies, along with monarchs, have bright colors on their wings, which serve to warn predators that they are toxic and should not be eaten.

Monarch butterflies are active during the day. North American monarchs migrate north and south each year. They may travel thousands of miles for their migration. When migrating, they fly alone; however, at nightfall, they come down to form a large group with other monarchs known as a roost or a bivouac. Roosts are often found in trees that will offer the butterflies shelter and protection from predators and the elements. They will also be located near a nectar source.

Habitat

The North American monarch butterfly, Danaus plexippus plexippus, can be found in different areas across the continent. There are both western and eastern populations of this species. Monarchs can be found between southern Canada and northern South America. This species has also been spotted on various islands, including Bermuda, the Cook Islands, Hawaii, Australia, New Zealand, Papua New Guinea, the Canary Islands, and the Solomon Islands.

Overwintering groups of monarch butterflies have also been found in Florida, Arizona, California, and Mexico. When choosing an overwintering location, monarchs look for a habitat that will provide them with access to streams, abundant sunlight, and vegetation. They also choose areas that do not have many predators.

When overwintering, monarchs may stay on different plants or trees, such as elms, locusts, oaks, sumacs, basswoods, cottonwoods, or mulberries. When monarchs are breeding, their habitats generally consist of trees, gardens, and residential areas. When breeding, finding an area with larval host plants where they can lay their eggs is important for the butterflies.

Diet

The diet of monarch butterfly larvae, or caterpillars, differs significantly from that of adult monarch butterflies. Monarchs lay their eggs on plants that the larvae will be able to eat after hatching. These host plants include California milkweed, woolly pod milkweed, poke milkweed, swamp milkweed, Arizona milkweed, butterfly weed, whorled milkweed, Caribbean milkweed, rush milkweed, and showy milkweed.

Adult monarch butterflies enjoy nectar from a variety of different plants. Some of these plants include milkweeds, teasel, coneflowers, alfalfa, lilac, tall ironweed, wild carrot, dame’s rocket, and Indian hemp. Monarchs also engage in mud-puddling, a behavior used to obtain moisture and minerals from wet gravel and damp soil.

Predators and Threats

There is growing concern that the monarch butterfly is increasingly threatened due to declining population numbers. As of 2014, the number of monarch butterflies that could be found west of the Rocky Mountains had declined by more than 90% since 1995. Another study released in February of 2015 by the U.S. Fish and Wildlife Service showed that almost one billion monarchs had disappeared from their overwintering locations since 1990.

One threat that has led to a decline in the number of monarch butterflies is loss of their habitats caused by the use of herbicides. Species of milkweed plants, where the monarchs lay their eggs and drink nectar, have been decreasing. More than 100 million acres of monarch habitat in the Midwest have been eliminated.

Another threat to monarchs is vehicle strikes. According to a 2019 study in northern Mexico, it was estimated that 200,000 monarchs were killed by vehicle strikes each year in just two hotspot locations.

In addition to these human-based threats to monarch butterflies, they also have some natural predators. However, their natural predators do not pose the same threat to the overall population of the butterflies that human-made causes do.

Even though many monarchs in both the larval and adult stages are toxic to many species, there are a few birds who have learned which parts are safe to eat. Other birds have developed the ability to identify which parts of monarchs are safe or unsafe to eat based on taste. Robins, sparrows, pinyon jays, orioles, thrashers, and some other birds prey on larvae and adult monarchs.

Other natural predators include mice, the Chinese mantis, the Asian lady beetle, and wasps.

Currently, monarch butterflies are listed as a Vulnerable species. Many scientists and others are concerned about monarch butterflies and their declining numbers. A review of their status was initiated by the U.S. Fish and Wildlife Service in December 2014.

Reproduction and Life Cycle

Male and female monarch butterflies usually mate several times. The more times they mate, the more eggs females will lay. Monarchs in overwintering populations typically mate in the spring. Unlike other butterfly species, monarchs are not as dependent on pheromones for mating.

When looking for a mate, male monarchs will find a female, follow her, and may even force her down to the ground. Once on the ground, the male and the female will often copulate and will stay attached to each other for between 30 and 60 minutes. However, not all mating attempts result in copulation. When a male and female monarch copulate, the male transfers both sperm and spermatophore to the female. The spermatophore gives additional nutrition to the female to help her lay more eggs.

Different factors can affect the size of the eggs a female will lay. Smaller females and those who are older typically lay smaller eggs than larger or younger adult females. Because females mate more than once, they may lay anywhere between 290 and 1,180 eggs throughout their lifetime.

There are four stages in the life cycle of a monarch butterfly: egg, larva, pupa, and adult. Adult monarchs lay their eggs on the underside of a leaf of a host plant, such as milkweed. The eggs are most often laid during spring and summer. Monarch eggs are very small. They are only about 1.2 x 0.9 millimeters and weigh less than 0.5 milligrams. The eggs are oval-shaped and light green or cream-colored. Once laid, the eggs will take between 3 and 6 days to finish developing. At that point, they will hatch.

The next stage in the life cycle of a monarch butterfly is the larval stage. More commonly referred to as caterpillars, larvae go through five different stages of growth. They start at just 2 to 6 millimeters in length, and by the end of the fifth stage, they are around 4.5 centimeters long. Between each of these stages, the caterpillar molts its skin. As the larvae progress through the five stages, they develop a distinctly white, yellow, and black striped pattern. During the fifth stage, the larvae eat a lot. By the end of the stage, they will have increased their weight by 2,700 times from when they first emerged from the egg.

Next, the larvae prepare for the third stage in the life cycle, which is the pupa stage. The caterpillar spins a silk pad where it can hang upside down. They attach themselves to their pad and form a J-shape. They stay in this J-shape for 12 to 16 hours, after which the caterpillar undergoes peristalsis. The skin behind their head splits, and they shed their skin. This leaves a green chrysalis or pupa. Over time, the chrysalis hardens and becomes less fragile. Inside the chrysalis, the adult butterfly forms. Shortly before the monarch emerges from the pupa, the chrysalis becomes translucent and eventually transparent.

Monarchs stay in the pupa stage for around two weeks. Once they emerge, they hang upside down to allow their wings to dry. The wings will dry out, stiffen, and expand when the butterfly pumps fluids into them. Once able to fly, the butterfly will find nectar to feed on. Adult monarch butterflies reach sexual maturity during the breeding season by the time they are four to five days old. Migrating monarchs will not reach sexual maturity until overwintering is finished, however.

During the breeding season, most monarch butterflies live between two and five weeks. The last generation of the season that migrates can live for up to nine months.

Monarch Butterfly Population

Monarch butterflies are listed as Vulnerable; their numbers have been decreasing due to threats such as habitat loss. There are currently between 14,500,000 and 127,900,000 mature individuals left.