The precipitous decline of the monarch butterfly population over the past three decades — estimates place it at more than 80 percent from the 1990s — has won a reprieve.
Data on monarchs overwintering in Mexico in 2022 show a sharp increase in their numbers, with researchers estimating monarch swarms covering 2.84 hectares (7 acres) compared with just 2.1 hectares (5.2 acres) the previous year.
Craig Wilson is director of the USDA Future Scientists Program and a senior research associate at Texas A&M’s Center for Mathematics and Science Education.
He’s also an expert on the monarch butterfly.
“The numbers came up 350 million,” Wilson said. “So there were pessimistic thoughts that it would not increase, but the 35 percent seems to be correct. The numbers were late coming out because I think data was being held up because of COVID down in Mexico or something, but they’re out there now.”
Epic journey
The migration of monarchs begins in Mexico’s oyamel fir forest, a 10,000-foot mountain aerie just north of Mexico City where the butterflies overwinter.
The trees in the forest provide an umbrella for the monarchs, keeping cold temperatures and precipitation off them as they try to retain fat reserves for the journey north in spring.
But habitat degradation, much of it due to logging, both legal and illegal, and land clearing for agriculture has put the butterflies at risk. The average amount of hectares occupied between 1993 and 2001 was 8.70. For the past decade, however, the average dropped to just 2.62 hectares.
Last year, Mexico officials reported the overwintering monarch population was down 26 percent from 2020.
“The increase in monarch butterflies is good news and indicates that we should continue working to maintain and reinforce conservation measures by Mexico, the United States and Canada,” said Jorge Rickards, general manager of World Wildlife Fund-Mexico. “Monarchs are important pollinators, and their migratory journey helps promote greater diversity of flowering plants, which benefits other species in natural ecosystems and contributes to the production of food for human consumption.”
The butterflies usually depart for points north around March 31, but in 2021 left earlier, around Feb. 21. Scientists aren’t yet sure if the early migration was a factor in the increase in the overwintering population this year.
“So they come down, it used to be March 31, the equinox, they’d start coming down the mountains from 10,000 feet in the sierra there north of Mexico City, the oyamel forest, they’d come down the mountain to get water and to mate, and then they make their way up through northern Mexico and into Texas and lay eggs on milkweed all the way,” Wilson said.
“And the problem is, there’s not enough milkweed.”
Milkweed’s key
And it just has to be milkweed, if you’re a monarch mom.
There are several species of milkweed which the butterflies find acceptable, but the native plants have been in decline for decades, attributable by many to loss of habitat and pesticide use.
The great freeze of 2021 was also a factor.
“Like this last year, because of the cold spell, my native milkweeds hadn’t come up in my pasture in Texas so I went out and bought 40 pots of tropical milkweed and scattered them around the seven-acre pasture and I had loads of eggs,” Wilson said. “I’d seen faded female monarchs trying to desperately lay eggs but there’s nothing to lay eggs on.”
The monarchs go through multiple generations on their migration north to the Midwest.
“So the idea is that those eggs hatch, the adult dies, the next generation hatches and stays about 28 days, flies up to Oklahoma and Kansas, lays eggs and dies, then the next generation makes it to the Midwest and lays eggs and dies,” Wilson said.
“The fourth generation there multiplies like crazy in the traditional breeding grounds of the Midwest and they produce a generation that is larger and stronger, and then Sept. 21 as soon as the migration starts, the inclination of the sun, following earth’s magnetic field — they have GPS in their antennae — and they will fly the whole 2,000 miles through the USA through northern Mexico and they will stop flying at the oyamel forest at 10,000 feet, and that’s the miracle,” he added.
How to help
Yet even miracles can do with a boost.
Over the past decade or so, a concerted effort to increase milkweed populations via plantings has been taking place in Texas and elsewhere, with TxDOT taking a high-profile role by planting milkweed at rest stops across the state.
Some cities, like McAllen, have taken a pro-active approach to help monarchs and other pollinators by taking the National Wildlife Federation’s Mayor’s Monarch Pledge as a commitment to preserving monarchs.
Mayor Javier Villalobos made the commitment in April, just like his predecessor, former mayor Jim Darling.
“McAllen is a Gold Star member and agreed to do all 25 items that are asked for, and that’s a nationwide program,” Wilson said. “And I encourage folks to approach their mayors to make their towns and cities monarch-friendly.”
But monarchs also need nectar, just like hummingbirds, for energy during migration.
“So wildflowers are great, things in your garden like lantana and verbena are idiot-proof perennials, so the monarch on its way south back to Mexico, or to Mexico, since it’s never been there, it needs the nectar sources,” Wilson said. “It does not need the milkweed, we don’t want it stopping to lay eggs. But when they migrate north in the spring you need both, the nectar plants for energy and definitely the milkweed, so that’s the critical thing.”
Individuals can buy milkweed to plant for the monarchs in fields or even in pots on your deck. Monarchs will find it, Wilson says.
“So things are happening,” Wilson added. “We have to be positive. But as for the trend continuing, there’s no way of knowing since conditions vary each year.”
