Monarch butterflies hang from trees in dense clusters in order to stay warm and provide shelter from the elements. Photo by Casey Amaral
Monarch butterflies hang from trees in dense clusters in order to stay warm and provide shelter from the elements. Photo by Casey Amaral
After hatching from eggs, monarch caterpillars feed exclusively on milkweed until they are large enough to develop a chrysalis. This diet protects the caterpillars and butterflies from predators to whom milkweed is poisonous. Photo by Calyse Tobias
After hatching from eggs, monarch caterpillars feed exclusively on milkweed until they are large enough to develop a chrysalis. This diet protects the caterpillars and butterflies from predators to whom milkweed is poisonous. Photo by Calyse Tobias
Visitors to Natural Bridges gaze up at the many clusters of monarch butterflies hanging overhead in the eucalyptus trees. A telescope gives them an up-close view of the thousands of brightly colored insects. Photo by Calyse Tobias
Visitors to Natural Bridges gaze up at the many clusters of monarch butterflies hanging overhead in the eucalyptus trees. A telescope gives them an up-close view of the thousands of brightly colored insects. Photo by Calyse Tobias
A female monarch butterfly perches outside of the Natural Bridges visitor’s center. This week, about 5,000 monarch butterflies have made a temporary home in Santa Cruz as they continue their annual migration. Photo by Casey Amaral
A female monarch butterfly perches outside of the Natural Bridges visitor’s center. This week, about 5,000 monarch butterflies have made a temporary home in Santa Cruz as they continue their annual migration. Photo by Casey Amaral

By Casey Amaral and Calyse Tobias

Every fall, thousands of monarch butterflies flock to Natural Bridges State Park as part of their annual migration. They fly great distances from southern Canada, Nevada, Arizona and valleys west of the Rocky Mountains in search of warmer weather. The monarch butterflies, Danaus plexippus, rest in a secluded Eucalyptus grove at Natural Bridges before completing their journey to Southern California and Mexico. The grove presents a sheltered and warm environment that is crucial for the butterflies, as they are unable to fly or even move once their body temperature goes below 55 degrees Fahrenheit. After the winter, the butterflies will migrate north and slightly inland to places like Salinas and San Jose. There, they will find more protection and natural habitats with their main source of food — milkweed. This is where they will lay eggs, beginning the next generational cycle.

Monarch butterflies are crucial pollinators for the ecosystem in Santa Cruz. However, about 90 percent of the monarchs have disappeared in the last 15 years due to climate change and the increased popularity of GMO plants. This season the Natural Bridges butterfly population peaked at about 7,000 butterflies, though about 2,000 have left to seek better shelter from the passing storm earlier in the week, leaving the population even more sparse. Efforts have been made to get monarch butterflies on the endangered species list.

Natural Bridges also hosts about 300 tours around this time of year, giving students opportunities for hands-on education about the life-cycles of the monarchs. A milkweed garden near the butterfly grove has larvae, caterpillars, chrysalides and butterflies for people to observe. The monarch butterflies will remain at Natural Bridges, Lighthouse Field and Pacific Grove from February to April.