The journey of monarch butterfly caterpillars

I was excited to find three small monarch butterfly caterpillars in my garden this week! We have been seeing the butterflies recently, and I hoped they would lay eggs on the milkweed leaves. These butterflies most likely migrated to east Tennessee from Canada; their offspring will make the long journey to the mountains of central Mexico in early October.

This tiny caterpillar will eat milkweed leaves for about 10 days. It will molt four times, increasing in length from 2mm at hatching to 30mm when it pupates. Before the final molt it will climb to a safe place to go through pupation.

During the chrysalis phase the caterpillar’s body becomes a “soup;” all the cells, except for the digestive tract, rearrange to form wings, a coiled mouth, antennae and a reproductive system. The beautiful jade green chrysalis turns black the day before the butterfly emerges.

It is hard to believe a delicate butterfly that weighs only half gram is able to make a flight of nearly 2,000 miles! Even more amazing, these butterflies have never made this trip before! The butterflies of this generation will fly to the mountains above Angangueo, Mexico, to overwinter in the oyamel fir trees. Most butterflies live only a month or so; the “Methuselah” generation that flies to Mexico delays reproduction so they can live six months. These butterflies begin to arrive in October and congregate on the trunks and branches of the fir trees. When tens of thousands of them form clusters, they cause the branches to sag and can even break them!

In late February or early March, the butterflies mate and the females begin their journey north. They fly to Texas and Louisiana to lay their eggs on milkweeds. The caterpillars that hatch make up generation 1, the butterflies they become are the ones we see in east Tennessee in April. Their caterpillars become generation 2. Those butterflies will fly to southern Canada to create generation 3. We are now seeing the third generation flying through and laying their eggs, the resulting butterflies will be the fourth generation that will begin their long journey south to Mexico.

My husband and I were fortunate to go on a tour to Mexico to witness this spectacle in January 2020. We learned that the butterflies use the position of the sun and magnetite crystals in their head to navigate to Mexico. Seeing millions of monarchs covering the trunks and hanging in clusters on the branches of the Oyamel Fir trees was awe-inspiring. Some of the butterflies were in flight. This is the only place that it is possible to hear the flapping of their wings!

Kris Light photographs wildflowers, animals and anything of interest with many of her best photos used in her website: click Search All Galleries to see photos. Her Outreach Science classes are available for public, private and homeschool groups through the AMSE. Kris welcomes questions at email.