milkweed

The American butterfly census

April 15, 2025 By EarthWise Leave a Comment

There has been a great deal of interest in the plight of monarch butterflies in this country. Monarchs’ population and migratory habits are closely watched, and many people have been planting milkweed in their gardens to help their caterpillars. But other butterfly species have received much less attention despite the fact that many butterfly populations are in decline.

A groundbreaking new study has provided comprehensive answers about the status of butterflies in America. Over the past 20 years, the contiguous US has lost 22 percent of its butterflies.

The study is based on over 12 million individual butteries counted in 77,000 surveys across 35 monitoring programs from 2000 to 2020. Three hundred forty-two butterfly species in total were analyzed. Thirty three percent showed statistically significant declines while less than 3% displayed statistically significant increases. Overall, 13 times as many species decreased as increased.

Why are butterfly populations crashing? Experts point to a combination of factors: habitat loss as land in converted for agriculture or development, climate change, and pesticide use. It is not clear which factor is most important and may well vary by location. Pesticide use – especially neonicotinoids – has been shown to play a particularly lethal role in studies.

Insects including butterflies play a huge role in supporting life on earth. They pollinate plants, feed birds and many other creatures in the food web. Nature collapses without them. And butterflies are clearly in trouble.

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See How Butterflies Are Surviving, or Not, Near You

Photo, posted August 9, 2016, courtesy of Rachel Larue/Arlington National Cemetery via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Confusion about monarch butterflies

February 9, 2024 By EarthWise Leave a Comment

For years, we have heard that the iconic monarch butterfly is in great peril. Monarchs east of the Rocky Mountains undertake a 4-generation, 3,000-mile migration in late summer to their winter home in central Mexico. Since the 1990s, the overwintering monarch colonies began a steep decline causing scientists to fear for the sustainability of the species. Trying to help, ordinary citizens have been planting milkweed – the food for the caterpillars – and have been rearing eggs and caterpillars on their porches and releasing adult butterflies.

A number of recent studies have rocked the world of monarch science. A growing group of scientists now believe that monarchs are not in fact imperiled and that the home rearing and commercial breeding of monarchs is actually a major threat to the butterfly.

According to a comprehensive 2022 study, there has been no sharp decline in Eastern monarch populations across their summer breeding range. The long-term declines in winter colony sizes are real but do not appear to be affecting the collective breeding population of Eastern monarchs.

An undisputed major threat to monarchs is a parasite known as OE, which weakens butterflies and also makes it unlikely for them to complete migrations. It turns out that overcrowding of butterflies resulting from the efforts of backyard and commercial breeders is increasing the spread of the disease. The butterflies are in need of social distancing.

Monarch scientists are split into two camps. One group calls for the protection of the butterfly under the Endangered Species Act. The other says that what monarchs most need is for us to leave them alone. It is a confusing situation.

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Rethinking Monarchs: Does the Beloved Butterfly Need Our Help?

Photo, posted October 1, 2021, courtesy of Renee Grayson via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Aphids And Monarchs | Earth Wise

September 15, 2023 By EarthWise Leave a Comment

Last year, the monarch butterfly was officially designated as endangered by the International Union for Conservation of Nature. Estimates are that the overall population of the species has dropped between 20% and 90% over the past several decades.

The migratory western population of monarchs is at the greatest risk of extinction, having declined by as much as 99.9% between the 1980s and 2021. Legal and illegal logging and deforestation to make space for agriculture and urban development has destroyed much of the butterflies’ winter shelter in Mexico and California and pesticides and herbicides throughout the butterflies’ range kills both the butterflies and the milkweed that their larvae feed on.

A new study by the University of Florida has found that aphids feeding on the milkweed that grows across the southern portions of the US causes the butterflies to lay fewer eggs on the plants and the caterpillars developing on those plants were slower to mature. The study showed that monarch laid three times as many eggs on aphid-free plants as they did on aphid-infested plants.

For years, there have been efforts to plant milkweed in urban areas to support monarch populations. However, aphids and other insect pests often reach high densities on plants in urban settings.

The researchers are advising home gardeners in the southern U.S. who want to conserve monarch butterflies to make use of safe techniques to limit aphid populations such as insecticidal soap. This may not always be an option and the researchers are investigating other options to keep aphids at low levels that aren’t harmful to monarchs.

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Aphids make tropical milkweed less inviting to monarch butterflies, study finds

Photo, posted October 12, 2018, courtesy of Renee Grayson via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Some Good Monarch News | Earth Wise

July 8, 2022 By EarthWise Leave a Comment

Eastern monarch butterflies spend their winter months in central Mexico. Every spring, they embark on a lengthy, multigenerational migration that takes them into the United States and even into southern Canada, where they breed. The butterflies go through several generations before they eventually migrate back to Mexico.

Twenty-five years ago, overwintering monarchs in Mexico blanketed nearly 45 acres of forest. The acreage covered, which has been surveyed annually since 1993, is a rough indicator for the actual number of butterflies that survive the difficult migration process. In 2013, the monarchs occupied only 1.6 acres of Mexican forest. The butterflies were deemed to be on the edge of extinction.

Last December, the monarch survey found 7 acres covered by the butterflies, an increase of 35% over the previous winter. The population appears to be steadily rebounding, although the numbers are still substantially lower than the levels seen in the 1990s.

The butterflies are struggling with multiple problems. There continues to be a lack of milkweed, the only food source for the caterpillars, in their breeding grounds along their migratory route. More extreme weather driven by climate change is another challenge, and illegal logging in their overwintering habitat in Mexico has also become a threat.

After the butterfly population crashed in 2013, conservation efforts shifted into high gear with lots of milkweed planting in the US and Canada, and crackdowns on timber poachers in Mexico.

The remarkable multigenerational migration of monarchs is a delicate phenomenon that can be disrupted by many different things. Eastern monarchs are still in serious danger, but the current trend seems to be positive.

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Warming Trends: Butterflies Bounce Back, Growing Up Gay Amid High Plains Oil, Art Focuses on Plastic Production

Photo, posted August 12, 2021, courtesy of Paul VanDerWerf via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

The Plight Of Monarch Butterflies | Earth Wise

April 20, 2022 By EarthWise Leave a Comment

The monarch butterfly is one of the world’s best-known butterflies and has become the symbol for a whole class of imperiled pollinators. Populations of the iconic orange-and-black insects have declined dramatically in recent decades.

According to the U.S. Fish and Wildlife Service, the eastern monarch population has dropped 88% between 1996 and 2020. Habitat loss, pesticide use, and global climate change are some of the factors driving monarch butterfly population declines.

According to a new study led by scientists at Emory University, monarch butterflies are also increasingly plagued by a debilitating parasite. The study, which was recently published in The Journal of Animal Ecology, reviewed 50 years of data on the infection rate of wild monarch butterflies by the protozoan Ophryocystis elektrosirrha (or O.E.). The research team found that the O.E. infection rate had increased from less than 1% of the eastern monarch population in 1968 to as much as 10% today.

The O.E. parasite invades the gut of monarch caterpillars. If the adult butterfly leaves the pupal stage with a severe parasitic infection, it begins oozing fluids from its body and dies. If the infection is lighter and the butterfly survives, it will not fly as well or live as long as uninfected butterflies.

The study found that one of the contributors to the rise in parasitism is the increased density of monarchs in places where they lay their eggs. The increased density may be due to several factors, including the loss of habitat, the widespread planting of non-native milkweed, and by people raising large numbers of monarchs in confined spaces.

If the infection rate continues to increase, monarch butterfly populations will likely continue to plummet.

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Web Links

Monarch butterflies increasingly plagued by parasites

Plight of the Monarch

Saving The Monarch Butterfly

Photo, posted September 18, 2008, courtesy of Roy Niswanger via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Cities And Monarch Butterflies

August 13, 2019 By EarthWise Leave a Comment

Monarchs are some of the most well-known butterflies in the U.S. It is well-known that populations of the iconic orange-and-black butterflies have been in a steep decline for the last 20 years. In fact, the Monarch population has declined by 80% over that period.

Milkweed, the only plant that Monarchs can lay their eggs on, continues to disappear across the United States and with it, the butterflies can disappear too.

Two new studies published in the journal Frontiers of Ecology and Evolution show that one of the most important things that can be done to save the Monarchs is to plant milkweed in cities.

We tend to think of cities as being the enemy of nature. But metropolitan areas actually matter for wildlife conservation and that is especially true for pollinators like butterflies that can actually survive with very small patches of habitat.

The new study estimates the amount of habitat in cities that is available to Monarchs and other pollinators and how much more can potentially be added. It looked at cities from the Monarch’s point of view by identifying the best places and most effective ways to engage land owners to transform low-quality green space – such as lawns – into high-quality homes for butterflies and other wildlife.

Just because urban dwellers can plant milkweed doesn’t always mean that they will. There has to be a public perception that milkweed and other native flowers are acceptable and beautiful elements in home landscaping. It will require some shifting of societal norms of what is desirable in neighborhood gardens in order for cities to be able to do their part in protecting butterflies and other species struggling in the modern world.

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