Monarch butterflies, who usually pass through town like so many other fleeting visitors, have taken up permanent residence at a 1200 square-foot milkweed garden known by local butterfly aficionados as “the Milkweed Patch” on the San Antonio River Museum Reach. The year-round colony is a first for San Antonio.
Resident Monarch butterfly on the San Antonio River Museum Reach
We’ve written about the Milkweed Patch here many times, but just this month the Patch gained national attention from Monarch researchers when it became one of hundreds of sites in the nation to be observed weekly by volunteer citizen scientists associated with the University of Minnesota-based Monarch Larvae Monitoring Project (MLMP).
Monarch butterflies traditionally pass through San Antonio and the “Texas Funnel” each spring and fall to and from their ancestral roosting grounds in the the mountains of Michoacan, Mexico. Year-round local Monarch butterfly communities are relatively common along the Gulf Coast, in Houston and in Florida, yet they’ve been unheard of in San Antonio–until now.
“Its historic,” says Mary Kennedy of Boerne, who monitors Monarch caterpillars, at Boerne’s Cibolo Nature Center and at Mitchell Lake. “We’ve never had anything
Mary Kennedy, volunteer at the Monarch Larvae Monitoring Project
like this before,” says the retired science teacher. Kennedy used Monarch butterflies in her classroom for years at Texas Military Institute. “This is not a place they would normally be this time of year.”
Kennedy suggests warmer winters and advantageous conditions at the protected, well-kept milkweed garden get credit for attracting the creatures that have captivated observers for millennia.
Dr. Karen Oberhauser, founder of the MLMP, calls the San Antonio Museum Reach Milkweed Patch “unique” and explains why scientists are especially interested in what goes on here.
“All Monarchs pass through Texas in the fall and again in the spring, and their use of resources in this state in many ways determines the success of the migration. Additionally, many Monarchs stay to breed in Texas in the fall, and understanding what drives this behavior will help us understand how monarchs might respond to climate change and how they are reacting to the presence of non-native milkweed. The site is particularly interesting because it is basically an island of habitat, and understanding what happens there will help us understand how monarchs use habitat patches of different sizes and with different amounts of isolation from other sites.”
Dr. Oberhauser also points out that the visibility of the Milkweed Patch in our highly trafficked River Walk will engage many more people in “the wonders of monarch biology.”
The first weeks of monitoring have yielded more than 30 chrysalises–17 alive and 15 dead–and some surprising results, says Kennedy. All butterflies were tested for Ophryocystis elektroscirrha, or OE, a nasty protozoan disease that infects Monarchs and other milkweed feeders. Some Monarch scientists have speculated that cultivating Monarch butterflies on Tropical milkweed year round can result in undesirable colonies of OE, which seems to flourish on the plant in southern climates late in the year. In colder climates and the wild, milkweeds die off in the winter, apparently purging OE to a large degree.
Kennedy was pleasantly surprised that not a single one of the Milkweed Patch Monarchs collected this month showed signs of the crippling, often fatal disease.
"A" marks the approximate spot for the San Antonio River Milkweed Patch
And San Antonians will be pleasantly surprised by a saunter to the Milkweed Patch. As the Spring Equinox approaches March 20, Monarchs will start to stream through San Antonio from Mexico, making their journey north and laying the first generation of eggs that will hatch, morph into their various stages, eclose and continue the multi-generation migration. Go take a look.
Directions: Park at the Pearl Brewery and cross to the west side of the River. Follow the trail about five minutes and watch for butterflies. You can also park on the deadened street at Elmira and Myrtle Streets, and descend the stairs to the River. Walk south about one minute and you’ll be there.
Like what you’re reading? Don’t miss a single post from the Texas Butterfly Ranch. Sign up for email delivery in the right navigation bar on this page, like us on Facebook, or follow us on Twitter, @butterflybeat.
texasbutterflyranch 
I was down there last month and tested 6 Monarchs for the OE parasite on behalf of the University of Georgia. It was really nice to see Monarchs here in January, but it does make one wonder, why didn’t these particular ones go to Mexico like the rest?
Lisa, worldwide some fall migrant monarchs naturally break reproductive diapause and seek out local milkweeds to lay their eggs. If humans deny them access to evergreen tropical milkweeds then those butterflies will search in vain and end up dying without breeding.
Why leave if there’s nectar, host plant and great weather? Thanks for writing, Lisa. What were the results of your OE tests?
Monika
The Sept & Oct. fall migrants that are in reproductive diapause will not let anything distract them (for more than a day or two) from their mission to migrate to the overwintering sites. This means no amount of nectar, milkweed or favorable weather will keep them from continuing to migrate. During November, however, the southward migratory drive wanes and by the end of November is kaput. Thus many 1000’s of monarchs get deposited north of the overwintering sites in Mexico in November. Of those, the portion that are still in reproductive diapause will seek shelter in trees and cluster if enough of them area around. And the portion that becomes reproductive will seek out milkweeds. Those that cannot find native milkweeds will die without breeding. If humans plant evergreen tropical milkweed (as was done at the San Antonio Museum Reach), they will lay eggs/patrol it and help produce a winter generation of monarchs, most of which appear to migrate north in the Spring.
I live in San Antonio – how can I help out? My schedule is flexible. I heard you speak at the AHTH GC. Love your blog
Thank you Gretchen! See today’s post with Mary’s email address. She is the hook-up for MLMP volunteers. THanks for stopping by.
Monika