Thousands of monarch butterflies provide a royal spectacle each fall as they travel through the Concho Valley.
“These are special insects, and they are moving through our country here in San Angelo in a big way,” said Dr. Charles Allen who is headquartered at the Texas A&M AgriLife Research and Extension Center at San Angelo. “There were literally thousands of them in the trees at the center here, probably 10,000 or more. And then a cold front moved through, and they’re all gone.”
Allen said San Angelo is a bit west of their annual migration route to Mexico with their main thoroughfare roughly paralleling Interstate 35 through Central Texas.
The butterflies at the AgriLife center, which covered the large pecan and oak trees in places more densely than the leaves, seemed fearless and remained undisturbed by the many birds in the area. Allen said that’s because they have a not-so-secret weapon, one of their two main features the entomologist said makes them special among all other animals.
“The monarch as a caterpillar feeds on milkweed. Along with nutrition, the larva obtains milkweed protective chemicals, which it holds within its body even as it changes into a butterfly. These chemicals affect anything that might want to eat it either later as a butterfly or as a larvae or caterpillar,” he said.
“The compounds don’t taste good, and birds eating them become sick, though they don’t die, so they quickly figure out that this brightly colored insect that’s floating peacefully through the air is not food, and they don’t eat them.”
“And not only will they not eat a monarch butterfly, they won’t eat anything that even looks like a monarch, so a number of insects have evolved to look just like a monarch because they are afforded the same respect and protection. That’s pretty special.”
But there’s something even more special about the monarch, Allen said. It’s their incredible 2,000-mile migration, which is unique in all of the animal kingdom.
“All the monarch butterflies we see and enjoy in our area, in fact all those across the eastern half of the U.S. winter in a small area of only about 10 acres southwest of Mexico City,” Allen said.
But if that is not incredible enough, Allen said the butterflies being seen headed toward Mexico now have never been close to Mexico, nor have their parents or grandparents.
He said each spring the monarchs leave Mexico heading north. They lay eggs on milkweed, the adults die, the eggs hatch, the larvae feed on the milkweed and become butterflies. This cycle occurs three more times as they head up through Texas, Oklahoma, Kansas, Nebraska and on up through Minnesota, Michigan and finally Canada.
“The ones that emerged in September in Canada are the ones we are seeing now here in San Angelo,” he said. “They are the world-class travelers, the ones now heading to Mexico. They are the great, great grandsons and granddaughters, four generations removed from those ancestors that started the cycle just last spring. So none of these butterflies or even the three previous generations have ever been to Mexico, a roughly 2,000 mile one-way trip. And yet with a ‘brain’ smaller than the tip of a fine pencil lead, they know right where to go.”
Allen said past experiments have purposely taken tagged butterflies 1,000 miles off course and even with that detour, they end up in Mexico on that roughly 10-acre plot.
“It’s just an amazing feat, and that’s another reason why monarchs are royal in my opinion,” he said. “No other insect or animal does that. Four generations out and they still know their way back to their historic overwintering grounds, a place this generation has never seen before. It’s an amazing story.”
But all is not well in the kingdom of the monarch, Allen said. Their numbers are falling, and the proof of that is easy enough to determine.
“The number of monarchs are determined by measuring that small acreage in Mexico. That’s done from photos taken from airplanes or even via satellite. They measure the size of the land area that turns from the green of the foliage to the orange of the butterflies as the insects arrive and roost on the trees. By this we know their populations are down significantly, over 90 percent, from what they were 15 years ago. Fortunately, during the last two years we have seen their numbers recover somewhat, but they are still less than 50 percent of what they were before.”
One of the reasons is they are dependent on very large-trunked old forest trees at their overwintering site, Allen said.
“Those large trunks or boles are heat sinks,” Allen said. “And when the occasional cold snap moves through the area, heat radiating from those large trunks enable the butterflies to survive.
“The area is a preserve and very dear to the people of Mexico who celebrate the butterflies’ annual return, which coincides with the annual Dia de Los Muertos or Day of the Dead celebration. The monarchs are said to represent the souls of departed ancestors returning for the annual visit.
“But that area has been plagued by illegal logging activities,” Allen said. “Hopefully, the attention in the media and elsewhere is bringing the plight of the monarch into focus and will help the Mexican government protect those trees that are so important to the survival of this species.”
In the U.S., Allen said, a lawsuit filed in early 2016 to declare the monarch a threatened species targets farmers use of genetically modified crops and herbicides associated with the loss of milkweed, the larvaes’ primary food source.
“It’s not a problem with the generation of monarchs that reproduce in Texas as we grow a lot of milkweed on our vast native ranges,” he said. “The problem comes with successive generations trying to reproduce once they reach the Corn Belt. Herbicides we are using there nowadays are really pretty effective on milkweed, so there’s less of a food resource than there once was.”
Allen said this issue is currently being countered by a wide array of programs and media attention since the word got out that this butterfly is special and at risk.
“Now people are planting lots and lots of milkweed along roadsides and really any kind of a little patch that’s not being used for something else,” Allen said.
“We’re seeing a groundswell of support now to preserve the monarch,” he said. “And I think if I’m a judge, we are experiencing some of that success right now as the butterflies move through our Concho Valley area. They’re migrating in huge numbers, and I’m going to be really surprised if the acreage in Mexico that’s colored orange does not show an increase now and hopefully for years to come for the regal and very special monarch butterfly.”