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Environmental Variables:  Decline of the Monarch Butterfly Population

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Environmental Variables:  Decline of the Monarch Butterfly Population

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This lesson will explore the effects of environmental factors such as climate changes, pesticides, and deforestation on the decline of the Monarch Butterfly population.

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6.LS2 #1: Evaluate and communicate the impact of environmental variables on population size.

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Temperature variations can lead to a decline in population size. This environmental cue triggers reproduction, migration, and hibernation. When these processes are disrupted, population stability is affected.

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US monarch butterfly population sees significant drop in last 2 decades

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Climate change can involve several situations but temperature change is the core component. Monarch butterflies depend on an optimal temperature range for every aspect of their life cycle progression including habitat and nutrition.

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Colder temperatures reduce the monarch population by changing migration paths and changing overwintering periods.

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Western Monarch Butterfly: Overwintering in California state parks

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Milkweed is a critical part of the Monarch's life. A decrease in milkweed will affect habitat and food causing a decrease in Monarch population.

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Monarchs and humans are vulnerable in a changing climate. Planting native plants not only creates monarch habitat, but also stores CO2.

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Female Monarchs lay eggs on milkweed so the caterpillar will have nutrition. A decrease in milkweed is not just a loss of habitat but it is a loss nutrition for the next generation.

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The Life Cycle of a Monarch Butterfly

The life cycle of a monarch butterfly starts when a female butterfly lays an egg on milkweed which is their host plant. The host plant is what the caterpillars will eat. The eggs are the yellow dots the arrow is pointing to.

A newborn caterpillar is 1/16 th of an inch long. The first meal for the caterpillar is the eggshell. After filling up its tiny body it needs to rest and molt. The skin on a caterpillar does not grow, so when they need a bigger skin suit, they spin a pad of silk, attach their hind legs into it, and walk out of their old suit. 111This process is called molting. If they are removed from the silk pad while molting, they will not be able to finish the process. This is why you should never move a caterpillar unless you see it moving. Move what it is on instead. The caterpillar will molt 5 times during its life and grows bigger each time. Each stage is called an instar.

The caterpillar on the right has just molted. You can see the old skin, looks like a black smudge, on the leaf. Notice how the tentacles are still folded up instead of extended like the one on the left? Also the head is bright yellow after molting. Caterpillars will usually eat the old skin so as not to leave a trace of having been there.

Caterpillars are eating machines and never stop eating unless it is time to molt.

The five caterpillars in the above picture are numbered to show you the difference in size between the different instars and how they double in size with each molting. The process between egg and caterpillar is roughly 18 days. Around day 18 the caterpillar is ready to form a chrysalis. It will crawl off of the host plant in the wild so that it will not be found by a predator. In a cage they will usually climb to the top and spin a pad of silk. They then attach their back prolegs into the silk and slowly let loose and hang in a J shape.

Notice how firm the tentacles are in this picture. They are straight and fleshed out when the caterpillar first forms the J shape.

Now look at these tentacles and notice that they are hanging like curled ribbons. This is what to look for when you want to see the caterpillar molt for the last time and for the chrysalis to emerge. This process is one that usually takes place in the early morning.

Finally the caterpillar straightens out, the skin splits at the head, and the green chrysalis case is finally showing. Notice the skin bunching up at the top by the silk pad.

The black spot at the top is the skin from the caterpillar. The chrysalis will swing back and forth or spin in a circle to get the skin to fall off.

And finally the skin does fall off and the chrysalis case smooths out. When it first forms it is a bright vivid green.

After one day the chrysalis has hardened and the color changes to a milky green with the gold markings. The butterfly will emerge from the chrysalis in a little over a week after it is formed.

The evening before the butterfly emerges you will see a change has taken place in the chrysalis and now the orange, black and white colors of the monarch appear. It will come out of the chrysalis case early the following morning after this color change takes place. The process of emerging from the chrysalis is called eclosing.

The butterfly will pop out of the chrysalis case and then hang on to it while it expands its wings.

Fluid in the abdomen is pumped into the wings to expand them. The process of expanding the wings will take several minutes.

Once fully expanded, the butterfly will hang in place until the wings have hardened up enough to fly. The butterfly will expel any excess fluid not needed for the process and it will be red and might look like blood. Don't be alarmed, it is not blood, the fluid is called meconium. All butterflies go through this same process.

It is easy to tell if you have a female or a male monarch. The male has a black spot in the center of the lower hind wings.

See the black spots on the hind wings? The veins are also thinner in the male than in the female.

The butterfly will eventually take its first flight. Butterflies do not need to eat on the day they eclose. Male and female monarchs will eventually find each other and mate. The females will search until they find milkweed to lay their eggs on and the process will start anew.

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The Life Cycle of a Monarch Butterfly - International Butterfly Breeders Association

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The Life Cycle of a Monarch Butterfly The life cycle of a monarch butterfly starts when a female butterfly lays an egg on milkweed which is their host plant. The host plant is what the caterpillars will eat. The eggs ... Read More

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The Monarch butterfly progresses through several generations while returning to their summer habitat. Pesticides are encountered throughout the migration causing damage to the population. During the summer months, deforestation occurs in their overwintering habitat or hibernation grounds. Efforts are underway to restore this habitat.

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Restoring Habitat for Monarch Butterflies | National Wildlife Federation

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From home gardens to sweeping grasslands, the National Wildlife Federation is engaged in restoring habitat for America's iconic monarch butterfly.

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The size of the population is a critical statistic for pollinators. The world depends on pollinators for our food supply. A decline in the pollinator population leads to fewer crops and less food. We must restore habitats and reduce pesticide use to help rebuild the pollinator population.