By Jan Wrede
Cibolo Nature Center

This month, Mary and J.J. Kennedy of Fair Oaks Ranch hosted a monarch butterfly researcher from the University of Minnesota. Reba Batalden was in Boerne studying monarch mating behavior as it relates to the presence of tropical and native milkweed plants during their fall monarch migration. She is a graduate student of Dr. Karen Oberhauser, an internationally known specialist on monarch behavior.

Reba told me that researchers have evidence that monarch butterflies save energy for their Herculean fall migration to Mexico by going into what is called reproductive diapause. In other words, they shut down their ability to reproduce. Makes sense, but citizen scientists at the Nature Center’s Milkweed Larvae Monitoring Project (MLMP) have some data that says this might not be altogether true.

In the Nature Center’s milkweed patch, our MLMP team of monarch enthusiasts check the native Antelope-Horn milkweed plants weekly. During the fall when monarch butterflies are migrating through Texas, we did not expect to see monarch eggs or larvae; however, both have been found on milkweed plants here and at other places in Texas too.

Antelope-Horn is a milkweed plant native to this area. Another milkweed species, the Tropical Milkweed, has also become a  popular and common Texas garden plant. Both Antelope-Horn and Tropical Milkweed are usually healthy in the fall and provide a good  source of monarch larval food at this time.

Reba set up an experiment in the Kennedy’s yard with four big, airy cages. Each held plenty of nectar and about 150 monarchs. She used 400 butterflies reared this summer in St. Paul, Minnesota and 250 captured in San Angelo, Texas during the fall migration. One butterfly cage contained Antelope-Horn, the second had another native milkweed called Hierba de Zizotes, the third held Tropical Milkweed and the fourth did not have any milkweed plants.

During the experiment, Reba took note of where the butterflies spent their time and if any were mating. She reports that in the Tropical Milkweed cage, the butterflies were constantly landing on the plants; whereas, in the cages with native milkweed, they would land on the plants less often. She also recorded a few pairs mating and laying eggs on both the Tropical Milkweed and native milkweed plants.

So, what might all this mean? Reba says that this new data gives us a more complete picture of the versatility of the monarch butterflies species. Although, most of the butterflies in her experiment were not actively reproducing during this migration time, some were! Her work verifies that this remarkable species has the behavioral diversity that allows a portion of the population to reproduce when a good food source is encountered during its fall migration.

Also, some of the adult butterflies in this experiment were taken back to the University of Minnesota to be tested for reproductive diapause. Others were where tagged and released by Mary Kennedy and fifth grade students at Kendall Elementary.

Mary Kennedy will rear butterflies from the eggs laid on the milkweed plants during Reba’s experiment. She plans to release  them and document the direction in which they fly. If they fly in a SSW direction, this will tell us that they are continuing their migration to the wintering grounds in Mexico. Stay tuned.