Monarch Butterfly Observers Expect Largest Migration in a Decade

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A Monarch butterfly is perched atop Tropical milkweed at a city pollinator garden along the King William Reach.

Scott Ball / Rivard Report

A monarch butterfly sits atop Tropical milkweed at a pollinator garden along the King William Reach.

Monarch butterflies are heading to San Antonio in a year that could claim the largest migration in a decade. 

Based on robust activity in the monarchs' primary Midwestern breeding grounds, Monarch Watch founder and expert Chip Taylor predicted "the migration should be the strongest since 2008." Taylor shared the promising outlook in a recent population update on the monarch butterfly conservation organization's blog

On Sept. 27, Journey North, a citizen science organization devoted to tracking wildlife migrations, reported a cold front pushing the leading edge of the migration south into Kansas and Oklahoma. The cool weather resulted in roosts in the Midwest that numbered up to 2,000 butterflies, with some vanguard monarchs already gathering in Texas.

Courtesy / Jerry Hatfield

A roost outside Lubbock on Sept. 30.

Jerry Hatfield, 400 miles north of San Antonio in Lubbock, reported a roost of "100 or more" nectaring on Gayfeather and hanging in clumps in the understories of trees Sept. 30.

All migrating monarch butterflies pass through the Texas Funnel in the fall. The migratory corridor plows through the state and channels the insects from Northern states into Mexico, where they roost in the mountains west of Mexico City. The following spring, they rouse from their diapause, reproduce, lay eggs, and die. The next generation starts the cycle anew, starting the migration through North America over multiple generations.

San Antonio lies in the heart of that migratory path and often serves as the first stop on the migration north in the spring and as the last stop in the fall.

Recent rains in the San Antonio area bolster optimistic predictions at a time when the U.S. Department of the Interior is considering the monarch butterfly for "threatened" status under the Endangered Species Act. The listing is scheduled for decision by June.

Local monarch butterfly fans are already seeing the early arrivals of this year's migration.

Cathy Downs, of Comfort, said she's "not seeing anything here yet, but I do have abundant nectar now in the area." Downs, who serves as a Monarch Watch conservation specialist, said she's confident the larger roosts of about 1,000-1,500 being reported in the Midwest will be able to develop sufficient lipid mass in Texas to "see their way clear to Mexico with nice, fat abdomens."

Monarch butterflies migrate through the Texas Funnel en route to and from their roosting grounds in Mexico in the spring and fall.

Courtesy / Nicolas Rivard

Monarch butterflies migrate through the Texas Funnel en route to and from their roosting grounds in Mexico in the spring and fall.

Migrating monarchs broke their diapause Sunday and left Drake White of the Nectar Bar on San Antonio's North Side "lots of eggs," White said. And monarch butterflies have been spotted regularly in ones and twos along the South Channel of the San Antonio River in the City's recently installed pollinator gardens.

Reports of Texas monarch sightings on iNaturalist, a citizen science website and app that allows ordinary folks to share observations of wildlife in real time, have been increasing steadily in recent days.

Peak migration season in San Antonio typically occurs during the last two weeks of  October.

As monarchs move through the San Antonio area, their primary need is nectar, so they can fuel up and build their fat reserves. Late season blooms such as mistflowers, purple coneflower, duranta, lantana, and salvias serve this purpose well.

While a large migrating population is a hopeful sign, it doesn't necessarily spell continued success for the monarch butterfly migration, scientists caution.

For decades, scientists have determined the health of the migrating monarch butterfly population by calculating the hectares the butterflies occupy at their overwintering sites in the mountains of Mexico. From November through March, millions of butterflies roost in the sanctuaries. The more forest area they occupy, the larger and healthier the estimated population.

That methodology, developed in the late 1990s, is being challenged as recent studies suggest that focusing on the migration's end-game results is a misleading metric for determining overall monarch butterfly migration health.

The monarch population has been estimated for decades by measuring the amount of forest occupied by the overwintering insects in Mexico.

Courtesy / Monarch Watch

The monarch population has been estimated for decades by measuring the amount of forest occupied by the overwintering insects in Mexico.

Climate change, disease, and the physical difficulties of migrating across a continent are presented as the monarch butterfly migration's greatest challenges in a recent paper in the journal Science. In it, Anurag Agrawal, chemical ecologist and author of Milkweed and Monarchs at Cornell University, uses the 2017 season as an example of how a stellar migration season doesn't predict a spectacular overwintering population or subsequent robust numbers of spring migrants.

"This has been one of the biggest years for summer monarchs in the Northeast and Midwest that most folks can remember over the past 20 [years]," Agrawal told the Rivard Report via email. "There was enough milkweed this summer. A huge number of butterflies – and the migration has begun. If the size of the overwintering population in Mexico is not much larger than the last couple of years, it would seem that something is wrong with the migration itself."

"They are doing well up here, but beyond that I am unwilling to predict the future," said monarch butterfly expert Karen Oberhauser, founder of Monarch Joint Venture and director of the Arboretum in Madison, Wisconsin. "Too much can happen between now and December." (Oberhauser will participate in a forum at the forthcoming Monarch Butterfly and Pollinator Festival on Oct. 19.)

Until monarchs arrive en masse in the area, the ongoing snout butterfly invasion that started in August continues, to the delight and annoyance of locals. Some folks find the creatures fascinating; others detest the mess on their car grilles and windshields.

According to Larry Gilbert, a professor of  integrated biology at the University of Texas at Austin, the two butterfly species have nothing to do with each other.

"Monarchs are independent of snouts," he said. "Not much overlap there."

11 thoughts on “Monarch Butterfly Observers Expect Largest Migration in a Decade

  1. How does a private school near Fiesta TexS connect with the city/county / TPW to create a habitat to support migrating monarchs

  2. For the last week we have had hundreds of Monarch butterflies on the north side of our Pecan tree in our back yard. They cover a huge area of the tree. They are beautiful. have taken video and pictures. I have never seen such a beautiful sight. One of the ranchers said he had seen hundreds and hundreds of them around his ranch.
    We are a small community 90 miles east of Lubbock and are thrilled to see them.

  3. I purchased a milkweed plant in spring (NJ). Monarchs are rare these days. With great joy, 4 catepillers finished off the plant. We had a cold spell, so I brought 3 crysylis inside and witnessed their birth. The 4th hid from sight, but I believe it emerged and before taking off, flew overhead. Next year, will be planting an abundance of milkweed plants.

  4. Monika: Just in time for your wonderful piece. Blue Star Contemporary is opening an exhibit this weekend inspired by the Monarch Butterfly.

    “MONARCHS: Brown and Native Contemporary Artists in the Path
    of the Butterfly.” I hope you review it for the Rivard Report. I got
    a sneak peak of the exhibit tonight. It’s an artistic cross-pollination delight.

  5. Saw 6 wild monarchs flying through town yesterday here in Prescott, Ontario Canada. It has been an amazing year for sightings and lots of activity in our designated milkweed fields.

  6. A slight bloom/leaf on our English Ivy has drawn hundreds if not thousands of Monarch Butterflies to our backyard today Oct 5, 2018. It has been a gorgeous sight. We live 38 Miles SW of Lubbock TX

  7. Still waiting for them to reach the Texas coastal and Houston area! Hope we see an increase. Unfortunately seeing posts in San Antonio that many are colliding with windshields. Believe it or not, I actually try to slow down if I can if I see them flying toward my car!

  8. I’ve had a great year here with the Monarchs!! I live on the Colorado River Arm of Lake LBJ, it’s just about an hour drive west of Austin, Tx. This year I increased my Milkweed to 60+ plants. At one time I counted 41 monarch catapillars feeding . Have had the pleasure of watching 3 emerge from their cryslis and watch them take flight. My goal for next year is to have over 100 Milkweed plants growing for them.

  9. I started growing milkweed in my backyard three summers ago. Last year my milkweed was not very tall and attracted no Monarchs to lay eggs. But this year it expanded and the milkweed grew four feet tall and we had dozens of Monarchs daily visiting and by mid August i noticed at least 50 eggs and i counted twelve caterpillars earing heartily. Then wasps took the caterpillars in an invasion that left me with 7 stings and ants took the eggs. I was so sad. But one morning i saw a female lay several eggs and i brought them all inside to raise (i was not going to helplessly watch wasps do that damage again) and five weeks later i have released 9 healthy Monarchs – 6 female and three male. Next year i will bring all eggs inside and scare the wasps away better. It has been the most amazing experience.

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