Monarch Butterfly

Reproductive Systems Research Task


They reside in lots of temperate and tropical open environments. However, as the both the adult and developing Monarch butterfly rely on milkweed as a source of food, they can be found in terrestrial environments such as meadows, fields, marshes, cleared roadsides, urban and suburban parks, gardens and trees. During winter, when they are in the period of hibernation, many of them can be found in fir, pine, oak, and cedar forests. During the winter, the Monarch butterfly faces many pressures such as logging of forests, clearance of agriculture, and coastal land development. Other threats include pesticides, which are used to kill insects which attack crops can be used to kill milkweed - one of the Monarch butterfly's sources of food. Ground-level ozone pollution can also damage or kill milkweed which is essential to the Monarch's diet.


Before the mating process, male and female Monarch's release pheremones in the environment which attracts animals of the same species but different sex. Once a male butterfly finds a female which has released pheremones, he will flap his wings rapidly and court the female in the air. He then tackles and breeds with her on the ground; linking their tails together and mate facing opposite directions. The male's reproductive organs are located in the abdomen and when the Monarch's start to mate, the end of the abdomen open up and wrap around the female abdomen. Once the male butterfly inserts his penis in the female, he deposits the sperm through the small pouch in her abdomen. Therefore, Monarch butterflies are cross fertilisers. Once the female lays her eggs, she will scatter them on a variety of plants which will provide food for the eggs when they turn into caterpillars. The fertilisation process is external. Organisms which are external fertilisers produce more offspring than internal fertilisers, however, many eggs may not even reach the zygote stage as they are usually eaten by predators. Out of 100 eggs that the female butterfly will lay, only about 2 percent will survive as a result of being consumed by other animals. An average  Monarch will lay several hundred.


Monarch butterflies are viviparous animals and have external embryo development as they are fertilised before their release. Their typical gestation period lasts for about 14 days and is generally temperature dependant. After 3 to 5 days, the caterpillar will emerge out of its egg by eating it from the inside and then eat the milkweed plant it has been laid on. The larvae stage lasts for 9 to 14 days, and during this time frame, many changes occur such as shedding of the exoskeleton and apparent growth in size. The caterpillar then climbs to a place to prepare for transformation into a chrysalis. Before transforming, it will rest for a few hours and eventually spins itself a small silk button and settle into a 'J' shape. After laying in this formation for 24 hours, it begins to change from the end and the larvae then turns into a light green colour with a  smooth texture. As the chrysalis is about to fully close off, the legs of the caterpillar falls off into a small pile, or sometimes a black cluster. The caterpillar stays in the chrysalis for about 10 days whilst it turns into various shades of green and the caterpillar turns inside out. After they have developed inside of the pupa, the butterfly eventually cracks open the clear shell, but will have wet wings. As the wings dry, the fluid is being absorbed into the wings which will soon create the smooth texture. This process of development is called metamorphsis. They typically live in meadows which have plentiful milkweed which is what Monarch butterflies live off to provide them with energy and nutrients. As Monarch butterflies are viviparous, they have various advantages such as not needing to waste time on caring for their young and not having to carry around extra weight on their body which slows down its movements. Laying of eggs is also fairly quick and easy, and the female doesn't need to go through labour. The female doesn't need to find extra food for her young and can continue her life in freedom. However, other disadvantages can include not being able to run away or be moved from possible predators. In some species then young will be very weak and frail when they hatch, and another problem arises when they aren't strong enough to break their own shell/egg. Some may not be raised properly as they have no parent to guide the young.

Parental Care

Monarch butterflies only have a life span of about a year, and lay several hundreds of eggs. This deems them as an R-Selection parent because of the large amount of  smaller sized offspring. However, unlike many of other R-Selection organisms, the Monarch butterfly has the ability to reproduce more than once. There'll typically be little amount of care as it will simply lay their egg then leave and wait for the next mating season to continue reproducing. The advantage of being an R-Selection species is that you can produce more offspring at a quicker pace and will have better survival skills; whilst the disadvantages are that they have a shorter mortality rate, and the energy made to make each is low therefore, they won't be as strong as K-Selection species. Another disadvantage would be the loss of offspring due to predators and other animals consuming the butterflies.

Other Interesting Information

  • An average Monarch Butterfly can lay up to 400 eggs
  • When developing, the caterpillars shed their skin up to 4 times
  • Up to 3 or 4 generations of Monarch's can be born in one summer season
  • A Monarch Butterfly's egg is about the size of a pinhead
  • Larvae(Caterpillars) can range from 1cm to 5cm in length
  • Some females leave a scent mark on the plant to tell the other females that she has laid eggs on there
  • Monarch Butterfly population is decreasing rapidly(refer to graph below)


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