Monarch Butterflies Rule Wildwood in Fall

orange and black monarch butterfly on yellow flower

Late August is the start of Monarch Butterfly season at Wildwood. When these butterflies arrive in Pennsylvania, they mate, and lay eggs. In 4-5 days, caterpillars hatch out of the eggs, eat the egg shell, and then start to eat the leaves. For 10 to 14 days, the caterpillars eat and grow, pausing 4 times to molt, or shed their skin.


The transition from caterpillar (larva) to chrysalis (pupa) is fascinating. The caterpillar roams around, looking for a place to pupate.

Caterpillar in a J

It spins a button of silk, and then hangs up-side-down from it, with its body in the shape of a “J”.

Caterpillar Chrysalis forming

The next day, the “J” relaxes and the skin pulsates. Suddenly, the skin breaks open and shrivels up, revealing a smooth, wet skin that gradually dries as it takes the shape of a chrysalis. The beautiful green chrysalis has stunning gold dots.

Chrysalis ready to open

Inside, the caterpillar transforms into a butterfly. After 10 to 14 days, the orange and black wing pattern starts to become visible and the large black abdomen makes the chrysalis look dark.

Monarch Butterfly emerges from Chrysalis

The chrysalis splits open, and the butterfly drops down, holding on by its legs. At first, the wings are small and shriveled. The fluid in the abdomen is pumped into the wings, making them expand. Eventually, the wings harden and in a few hours, the butterfly is ready for its first flight.

Usually, the cycle continues with the newly emerged adults laying eggs. But the monarchs of fall have a different fate. They can’t survive freezing temperatures in any stage: egg, caterpillar, chrysalis, or adult. So the adults that emerge in September and October defer reproduction and instead, migrate to Mexico. Gathering by the thousands in fir trees high in the mountains not far from Mexico City, they spend the winter using as little energy as possible.

Monarchs Need Milkweed


Monarchs will only lay their eggs on milkweed plants. Not many animals can tolerate eating these leaves because the thick, milky sap gums up their jaws. But monarchs manage just fine. The sap contains a cardiac glycoside, which is poisonous to birds and mammals. As the caterpillars eat, they use the nutrition to grow and they incorporate the toxin into their skin. The toxin stays there throughout the life cycle. The dramatic orange and black pattern serves as a warning that advertises “Caution: Stay away!” Birds or mammals that try to eat a monarch will gag, spit it out, and never try to eat anything similar again.

There are several species of milkweed; monarchs can use any of them as a host plant for the caterpillars. In our area Common Milkweed, Butterfly Milkweed, and Swamp Milkweed are popular. Planting milkweed will help the monarchs reproduce, while flowers with nectar provide the food the adult butterflies need to fuel their migration.

Tagging Monarch Butterflies

Tagged Monarch Butterfly

North American scientists didn”t find the winter roosting location of the monarchs until the 1970s. There are still questions to be answered about the migration. A citizen science project called Monarch Watch helps by gathering data on the butterflies and their migration.

Tagging Monarch Butterfly

Wildwood Park participates in Monarch Watch, tagging butterflies that are raised in the nature center or caught in the park. Before release, a sticker is attached to the wing. Each tag has an email address and a unique number. The date, tag number, sex, and location are recorded on a data sheet. All the information is sent to a database for scientists to use. Anyone who finds a tag reports the number, date, and location, helping scientists understand the migration.

How Wildwood Helps Monarchs

inside the Wildwood Nature Center

The park has milkweed growing in several areas to host monarch caterpillars, and nectar plants for adults. The nature center has a special exhibit every fall. Monarch caterpillars gathered in the park are raised in a Plexiglas container. Visitors can watch them eating milkweed and if they are lucky, may even see a chrysalis form or a butterfly emerge. Because these caterpillars are raised indoors, they are protected from predators that include insects and spiders.

Wildwood Park participates in Monarch Watch, tagging up to 50 monarchs each fall. In 2015, one of the monarchs raised in the nature center and tagged before it was released was recovered in El Rosario Preserve in Mexico.

At an annual festival called Celebrate Wildwood, the monarchs are on display for hundreds of visitors, who learn about these fascinating insects. They take home milkweed seeds to plant, encouraging monarchs in their own yard.

Things You Can Do To Help Monarchs