butterfly

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

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

The American butterfly census

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Aphids And Monarchs | Earth Wise

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.

Web Links