Western insect population sees increase in 2021
The International Union for Conservation of Nature placed the monarch butterfly on its Red List of Threatened Species as endangered in July, but despite decades of decline, the population of this delicate insect has rebounded in 2021.
Invertebrates aren’t often the first animals to gain sympathy from people when their populations dwindle, but pollinator conservation awareness is growing in popularity. In Colorado, the summer destination of the migration routes of two monarch populations, people may be clinging to the idea of growing native plants on lawns, avoiding pesticides and supporting birds and wildlife. native invertebrates.
The monarch butterfly, or Danaus plexippus, is something of a charismatic poster child for pollinating invertebrates, said Amanda Kuenzi, director of community science at the Mountain Studies Institute and president of the Southwest Chapter of the Colorado Native Plants Society.
“They are tall, beautiful and recognizable. But what it really comes down to is that we are in a pollinator crisis on a global scale,” she said.
The monarch butterfly population has been in steep decline for decades, dropping up to 90% in the past 30 to 40 years, she said. The IUCN in Switzerland attributed its designation of the endangered monarch butterfly to habitat destruction and climate change.
The monarch is currently not listed as an endangered species under the US Endangered Species Act – meaning it does not qualify for federal protection or funding – but it should be reassessed in 2024 by the US Fish and Wildlife Service.
In 2020, the Fish and Wildlife Service announced that “listing the monarch butterfly under the Endangered Species Act is warranted but precluded,” according to the Butterfly Pavilion in Denver.
Monarchs that overwinter in California and migrate to Colorado for the summer have grown from a population of just 2,000 in 2020 to 200,000 in 2021, according to data from the Colorado Butterfly Monitoring Network organized by the Butterfly Pavilion.
Shiran Hershcovich, a lepidopterist at the Butterfly Pavilion, said it was too early to tell if the monarch population had paused, and while the increase in population size recorded last year was exciting, its cause remains a puzzle for scientists.
“Booms and busts are not uncommon in the invertebrate world,” she said. “Many insect species will have large types of cycles in their populations. But not as dramatic as what we saw with the monarch butterfly last year.
The increase in population size hasn’t brought the monarch butterfly back to its former numbers, but Hershcovich sees the development as a sign of hope.
“We are very interested in what the data will show this year. In Colorado, we reported a 180% increase in monarch sightings. Which is also consistent with reports from across the country,” she said.
Dangers and Benefits for Butterflies
Scientists have several high-profile theories about how monarchs could make a comeback.
For starters, environmental pressures such as pollution of native ecosystems and environments could have been reduced by slowing human activity during the COVID-19 pandemic.
Another theory is that Colorado’s fire season started late this year and the state received a fair amount of moisture, at least by milkweed standards. Milkweed is a perennial flowering plant that monarch larvae, or caterpillars, feed on almost exclusively, Hershcovich said. And if it is reduced to ashes, it cannot be eaten by butterfly larvae.
Smoke from wildfires can also threaten monarch butterflies.
“Butterflies are very sensitive to environmental cues. So fire seasons can also be very difficult for butterfly populations,” she said. “Butterflies also sense the world differently than we do, so they can pick up many chemical cues from the environment that we humans aren’t as sensitive to.
Thick smoke can disrupt or confuse a butterfly’s senses, so scientists theorize wildfires could have drastic effects on a species’ population.
Milkweed is also a riparian species, which means it needs lots of moisture to grow and thrive, Hershcovich said.
“Caterpillars are often very, very picky and only eat a very specific plant or a very specific group of plants, such as monarch butterflies and milkweed,” she said.
If milkweed is not present in a monarch’s environment, the butterfly will not bother to lay eggs because the next generation will not be successful.
But Hershcovich said humans are also doing their part to help the monarch population.
“Pollinators in general are kind of in a frenzy right now,” she said. “They’ve been in the spotlight a lot more. There has been a lot more advocacy for pollinator health. So there have been many more people involved in invertebrate conservation and monarch conservation than ever before.
People have moved into their own backyards to support monarchs and other pollinators by planting milkweed and other native flowering plants, she said.
But, she warned, it’s too early to say for sure how Colorado’s monarch population will fare in the future.
Kuenzi said she has spotted more milkweed “than ever” in the Durango area than in recent years.
“I feel like people get the message,” she said. “I don’t know if it’s intentionally planted or who does it or what, but I noticed there are some milkweed plants popping up along the river trail.”
She said the local milkweed would do even better with wetter habitat. But anywhere there is runoff, such as along the banks of a river or road where the water will flow downstream, is a good habitat for the plant.
Still, Kuenzi cautioned that people shouldn’t adopt the misconception that milkweed is the only plant the monarch species needs. After their larval stage, they need a multitude of wildflowers to draw nectar from.
She said the increased focus on monarch conservation is good for all pollinators – a rising tide lifts all ships.
But Hershcovich warned that although the outlook for monarch butterflies appears optimistic, there is not enough evidence to say definitively that they are truly recovering from years of population decline.
“So is this a trend? Will we continue to see populations increase? Was it a one-time event? Will we see a decrease? It’s a bit too early to tell what’s going on in terms of the model,” she said.
She said Colorado is a unique place for monarchs because it is the epicenter of two monarch “communities” with distinct migration routes.
“Monarch populations are divided into two groups: the eastern monarch and the western monarch,” she said. “The eastern monarch is the larger of the two. It spends its winters in Mexico. So he makes that long trip south to spend the cold months there.
“The Western Monarch will spend its winters on the California coast. Colorado is actually where these two monarch populations are split,” she said. “So all monarchs – and this is more of a general rule – but most monarchs east of the Rocky Mountains belong to the eastern population of monarchs and will migrate south for the winter. And then the monarchs west of the Rockies belong to the western monarch population and will spend their winters in California.