This week’s cool front should push migrating monarch butterflies south into San Antonio on their path to Mexico, scientists and citizen scientists report. What the insects find here depends on which route they take.

Texas’ late summer drought has decimated the usual nectar sources on which monarch butterflies and other insects depend. Monarchs load up on nectar to bolster their fat reserves to fuel their flight to Mexico and sustain them through the winter.

Reports on citizen science platforms such as Journey North, iNaturalist, and the DPLEX list, a monarch-butterfly email list operated by the University of Kansas, have been optimistic about high monarch numbers in the Midwestern breeding grounds all summer. Yet unfavorable conditions in Texas could have a negative impact on the migration.

“Having a drought in Texas during the fall would in theory be problematic for the migration,” said Andy Davis, research scientist at the University of Georgia’s Odum School of Ecology and editor-in-chief of the open-access scientific journal, Animal Migration.

Davis explained that if the number of monarchs that arrive at the Mexican colonies where they spend the winter are unexpectedly small despite a robust summer breeding season, “we might be able to tie it to the Texas drought.”

One of the 2019 season’s first overnight roosts in Texas was spotted west of Fort Worth earlier this week.

“They came in this evening and are roosting on one of the oak trees,” the observer in Cisco reported on the citizen science platform iNaturalist on Oct. 6. “… A cool front is supposed to be coming in tonight so they may be flying ahead of it.”

An Oct. 8 story in The Washington Post reported a “front full of butterflies” sweeping through Oklahoma City last weekend. The peak migration period for San Antonio’s latitude typically runs from Oct. 10 to Oct. 22, but some argue that the peak might occur later given the changing climate.

Throughout September, reports from Canada, Maine, and into the Midwest have touted large numbers of monarchs. To follow the migration in real time, check out Journey North’s live monarch migration tracking map.

Monarch butterflies start their migration in Mexico, often laying their first round of eggs in Texas. Multiple generations move north over the summer all the way to Canada, then return south in the fall, moving through the Texas Funnel en route back to Mexico. Credit: Courtesy / Monarch Watch

But as Davis and others have pointed out, much can happen between now and the time the butterflies arrive at their destination in Mexico, typically about three weeks from now.

Wildfires, hurricanes, a lack of nectar in Texas and northern Mexico, and pesticide applications pose myriad hazards to the migrating insects and could derail what appears to be a banner year.

In the Texas Funnel, the migratory corridor through which all migrating monarchs must pass on their way to Mexico, widespread drought has been interrupted by spotty, occasional thunderstorms during summer and into the fall. September was the hottest in history and the usual first cold front was about two weeks late.

Texas is critical to the migrating insects in the later stages of their migration since it is where they fuel up and build the fat stores that will get them through the winter in Mexico.

Jenny Singleton, a longtime docent for Grapevine’s Butterfly Flutterby Festival, has been tagging monarchs for decades at her family’s ranch along the San Saba River in Menard County. A recent visit left her concerned. “Everything is dried to a crisp,” she said. “It’s scary how hot and dry it is.”

“Much of our Texas Hill Country is extremely dry,” said Charles Bartlett, botanist and president of Greenhaven Industries Inc., a San Antonio landscaping company that specializes in rural and urban pollinator habitats. “Many areas just west of San Antonio have not seen any appreciable rain in more than 90 days. … Sunflowers and other native plants are dry and supplying no nectar or pollen for bees and butterflies.”

Bartlett added that he’s seen only a few monarchs in the Hill Country to date. Usually, the area gets a “pre-migration migration” of monarchs around Labor Day in early September. That didn’t happen this year.

Cathy Downs, a Comfort-based monarch outreach specialist for citizen science tagging organization Monarch Watch in Kansas, agreed that local monarch sightings have been sparse to date. “Not seeing anything in Kendall County,” said Downs. “We’ve had .2 inches of rain since June.”

Reports this week on iNaturalist had monarchs veering more toward far West Texas, where drought conditions are less severe than in the Hill Country, said Downs.

Bartlett and Downs pointed out that dry conditions in the Hill Country make pollinator habitats in urban settings even more important than usual. Late season nectar plants such as fall asters, purple mist flower, copper canyon daisy, pentas, and Turk’s cap can help fill the void. “And mulch, mulch, mulch,” said Bartlett.

San Antonio Report co-founder Monika Maeckle writes about pollinators, native plants, and the ecosystems that sustain them at the Texas Butterfly Ranch website. She is also the founder and director of...