The Fascinating Biology of the Monarch Butterfly

Topical Tuesday – Nature

The monarch butterfly is not only beautiful but is also a fascinating biological study. Consider the following Monarch facts:

 Monarch just hours after emerging from it chrysalis

Monarch just hours after emerging from it chrysalis

1. It “tastes bad” to predators.
2. Because it tastes bad, it is mimicked by the Viceroy butterfly that does not taste bad, but is avoided by predators because it looks like the Monarch.
3. There are four generations every year, but they start and stop in the same area after migrating all over North America.
4. The larvae live on milkweed, which is toxic to most other insects.
5. Each of the first three generations typically live about two to three months, but the fourth generation lives up to six months.
6. They migrate great distances, from Mexico into Canada and back


The Viceroy mimics the Monarch. (Note the curved band across the veins in the wings)

The Viceroy mimics the Monarch. (Note the curved band across the veins in the wings)

There are many examples of mimicry in nature. There is red-black-and-white banded harmless and beneficial king snake that mimics the poisonous coral snake that most animals (including people) avoid. There are insects whose bodies resemble dead leaves and fish whose bodies resemble coral. Mimicry enhances survival.

The viceroy butterfly is the classical example of mimicry: it works this way. The monarch apparently tastes bad. Birds that catch a monarch soon let go of it and avoid them in the future, enhancing the monarch’s survival. Nature has adapted the viceroy butterfly to look like the monarch, enhancing its survival because it is also avoided by those same predators that cannot tell the difference between the two. It takes an informed human eye to detect the difference between the two butterflies. The viceroy has a curved stripe that crosses the main dark stripes in the wing. The monarch does not have that horizontal stripe.


A Fifth Instar Monarch Caterpillar—head to the left (Photo: Source Letting milkweed grow

A Fifth Instar Monarch Caterpillar—head to the left (Photo: Source Letting milkweed grow

The Monarch goes through four generations every year. In the spring, the first generation hatches from eggs laid by the butterflies that flew south at the end of the previous year. They migrate (fly) from the overwintering sites in Mexico and Southern California and fly north as far as Canada. Over the summer, two more generations, living hundreds to a thousand miles from the southern range, grow from eggs to mature adults, and die. Their life-spans are about is about two months. The fourth generation appears toward end of the summer and will migrate to the southern overwintering sites. This fourth generation also lives up to seven months rather than the two months of the first three generations of that year.

One of the most remarkable aspects of this life cycle is that the fourth generation adults return to the same over-wintering areas of their great grand parents that they have never seen.

Life Cycle

The Monarch butterfly Chrysalis (Photo: Greyson Orlando, Wikipedia)

The Monarch butterfly Chrysalis (Photo: Greyson Orlando, Wikipedia)

Adults lay their eggs on milkweed plants, which the larva (caterpillar) prefers. The sap of the milkweed contains a latex compound that makes it poisonous to many animals. Monarch caterpillars are adapted to tolerate the latex.

The Monarch larva or caterpillar goes through five stages (called instars). As the caterpillar grows, at the end of each instar, it sheds (molts) and usually eats the shed skin. After the fifth instar, the caterpillar spins and attaches a silk pad to a suitable support. It then hangs from this pad holding on by its last pair of prolegs (prolegs are the legs of a caterpillar before it becomes and adult).

Hanging upside down, it molts into a translucent green chrysalis. (Note: moths spin a cocoon while butterflies produce a chrysalis.)
After two weeks, the adult butterfly emerges from the chrysalis. Fluid is pumped into the veins in the wings causing them to stretch and harden. Soon, it is ready to fly.

Adult Monarchs feed on nectar of many flowers.

Monarchs are known for congregating in huge flocks, especially in their overwintering sites. In addition to providing access to suitable mates to begin the first generation, these gatherings also serve to protect the species from predators. By gathering en mass, predators may take a number of individuals, especially those on the edges of the flock, but cannot consume all of the butterflies. Leaving a group to reproduce, starting the cycle over with the next “first generation” of the new year.

A Monarch shortly after emerging from its Chrysalis (visible to the left of the butterfly)

A Monarch shortly after emerging from its Chrysalis (visible to the left of the butterfly)

Kingdom: Animalia (Animals)
Phylum: Arthropoda (Invertebrate animals typically with jointed legs and exoskeletons)
Class: Insecta (Insects)
Order Lepidoptera (Butterflies and Moths – 180,000 species)
Family: Nymphalidae (largest family of butterflies – about 6,000 species)
Genus and Species: Danaus plexippus – (Scientific name)

A Note About Taxonomic Nomenclature:
Taxonomic classifications from “Kingdom” through “Order” are capitalized, but not italicized, even though they are written in the classical Latin nomenclature. The Genus, species, and subspecies are always italicized. Only the Genus is capitalized.
Also, to be precisely correct, the common name of an organism (e.g., “monarch butterfly”) is not capitalized. Some authors will capitalize the common name if it is the subject of the written work.

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2 Responses to The Fascinating Biology of the Monarch Butterfly

  1. PositivelyUnbroken says:

    Where I live in New Hampshire, there is much development that interferes with the natural habitat of the Monarch. When my children were younger, we would make it our summer mission to save as many Monarchs as possible. We would go out and search the tender sprigs of milkweed that would pop up in the lawn between mowings. That tended to be where the butterflies would lay their eggs. We would then bring the eggs in, watch them hatch into caterpillars, and “raise them” into butterflies when we would let them go. One summer (back when I might have been crazy…), we “rescued” and ultimately released 46 Monarch butterflies that we raised from eggs. Thank you for bringing attention to these beautiful creatures!

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