Ed Yong: Reared Monarchs Don't Migrate

The Altantic:

By testing monarchs bought from a commercial supplier, Ayse Tenger-Trolander from the University of Chicago showed that they make terrible migrators. While their wild counterparts have a strong tendency to head south, the mail-order insects flew in random directions. Tenger-Trolander also found that wild monarchs became similarly inept if she raised them indoors, even if she tried her best to mimic natural conditions.

“It’s a powerful study,” says Sonia Altizer from the University of Georgia, a monarch expert who was not involved in the research. “It’s the first to definitively show that captive-bred monarchs won’t show the same orientation behavior that wild ones will.”

Selecting individuals to rear leads to domestication; domestication leads to trouble.

Michael J. Coren: Monarch Butterflies in the West


There’s not much to be grateful for after the great Western Monarch Thanksgiving Count this year. The three-week volunteer effort in California dispatches scores of volunteers to hunt in their woods, backyards, and fields in search for the colorful migrating butterfly. This year, signs of trouble came early.

Far fewer of the insects were heading south this year, and those that have arrived did so a month late, according to Xerces, a non-profit conservation group for invertebrates. One researcher said it was the fewest monarch butterflies in central California in 46 years. Surveyors at 97 sites found only 20,456 monarchs compared to 148,000 at the same sites last year, an 86% decline. It’s possible more insects will make the journey late this year, says Xerces, but that now seems unlikely.

Diana Gitig: New Hypothesis about Declining Monarch Butterflies

Ars Technica

Anurag Agrawal ... has written a book about them called Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution. Monarches and their sole food source, the toxic milkweed plant, provide a great example of coevolution. Monarch caterpillars are born on milkweed leaves, where their mothers deposited them as eggs. They grow fat eating the plant. They are not pollinators; the milkweed gets nothing out of the relationship. In fact, the plant goes to great lengths to fight the monarchs. Milkweeds exude latex (the “milk” responsible for the eponym), which contains a noxious chemical cocktail suspended in the sticky rubber. A newly hatched monarch caterpillar’s teeth and feet can, and often do, get easily mired. “More than 60 percent of monarchs died in the burst of latex that accompanied their first bites into the plant,” Agrawal tells us. “Less than 10 percent make it to full size.”

Because monarch butterflies are disappearing. They have experienced a 75-percent drop in their numbers over the past 25 years, and a number of reasons for this decline have been suggested. One is that their overwintering grounds, already quite small, are being threatened by logging, hunting, cattle grazing, and climate change.

But the prevailing idea is that monarchs are disappearing because milkweed is disappearing due to urbanization, the expansion of agriculture, and especially the indiscriminate overuse of herbicides enabled by the advent of herbicide-resistant crops. Monarch caterpillars have nothing to eat, this idea goes, and so they die.

Despite the popularity and the appeal of this hypothesis, Agrawal does not buy it.

Luke Runyon: Causes of the Monarch Butterfly Decline


Monarch butterflies are disappearing. Populations of these distinctive black and orange migratory insects have been in precipitous decline for the past 20 years, but scientists aren’t exactly sure what’s causing them to vanish.

So far, potential culprits include disease, climate change, drought and deforestation. Everyone from loggers to suburban developers has been implicated. But much of the blame has been placed on farmers and the pesticides they rely on — pesticides that have reduced the milkweed that monarch caterpillars feast on. Now, however, scientists say that may not be the full story.

Every spring, hundreds of thousands of monarchs sweep across the Great Plains from Mexico to Canada, and then back again in the fall. It’s an amazing journey, one that takes place over multiple generations for the butterflies. The insects breed while traveling north, expending four generations to make it to Canada. The final generation then flies all the way back to Mexico to spend the winter there.

Monarch populations are measured in hectares (roughly 2 1/2 acres). Surveys of their wintering habitats in the central mountains of Mexico show dense populations of monarchs at an average of more than nine hectares during the winters from 1995 to 2002. In 2014, monarchs took up less than one hectare.

Scott Johnson: Monarchs at Peril


Monarch butterflies could disappear from Eastern US within 20 years. As population declines, the prognosis is not encouraging.

In colder climes, signs of spring can lift a heavy weight from a tired, frozen spirit. Trees bud, flowers bloom, and migratory species trickle in to announce the approach of summer. In the US, one of those species is a floppy orange gem: the monarch butterfly. These insects winter in amazingly dense clusters in Mexican forests before making a staggeringly long journey (one that spans multiple generations, in fact) to summer homes to the north.

But in recent years, the population of monarchs that stay east of the Rockies has dropped like a rock. Precise population numbers are difficult to come by, but estimates kept by the US Fish and Wildlife Service show about an 80 percent decline over the last decade.

Monarch Migration and Genetics


Jaap De Roode, Emory University

Jaap De Roode, Emory University

To understand the evolutionary origin and genetic basis of these two hallmark monarch traits, a team led by Marcus Kronforst from the University of Chicago and Shuai Zhan from the Shanghai Institutes for Biological Sciences sequenced 92 Danaus plexippus genomes from around the world — including non-migratory and white varieties — as well as nine closely related species.

They found that monarchs are ancestrally migratory. These butterflies are predominantly a North American species, though their broad distribution now includes South and Central America and Western Europe. The team traced the lineage back to a migratory population that likely originated in the southern U.S. or northern Mexico. The butterflies then dispersed out of North America in three separate events: to Central and South America, across the Atlantic, and across the Pacific. In all three cases, the butterfly lost its migratory behavior; only North American monarchs migrate.

Much to learn you still have…my old padawan. This is just the beginning to better understand our Monarch friends.

Monarchs on Radar

John Metcalfe, writing for CityLab:

Michael Warwick; Shutterstock

Michael Warwick; Shutterstock

Meteorologists in St. Louis noticed a cloud acting peculiarly: It was beating a path toward Mexico while changing into a variety of odd shapes. Was it a radar glitch? The debris signature of a south-moving tornado?

The answer was more heartening—and bizarre. After analyzing the reflections, the National Weather Service concluded they showed an immense swarm of Monarch butterflies migrating to their winter home in the Mexican mountains.
NWS St. Louis

NWS St. Louis

May the Force be with you.

Decline of Monarch Butterflies Linked to Agriculture

Kate Prengaman, writing for Ars Technica:

The massive migration of monarch butterflies is amazing—the insects go from grazing on milkweed plants as caterpillars in the midwest to spending winters in Mexico. But Monarch populations have been on the decline for some time, with a variety of factors being considered: lost habitat in Mexico, damage from pesticides, or climate change.

Conservation strategy for a species that traverses thousands of miles is complicated business, so a team of scientists from the University of Guelph decided to sort out which factors were the most responsible for the monarch’s population declines—changes at the breeding grounds, the wintering sites, or climate changes.

Their conclusions suggest that we can’t blame deforestation in Mexico for this environmental problem. The monarchs are suffering from a lack of milkweed, the only plant the caterpillars eat. In fact, a model built by the researchers suggested that monarch populations were four times more sensitive to the loss of milkweed on their breeding grounds than the loss of the forested habitat in which they spend the winters.
William Warby

William Warby

When you look at the dark side, careful you must be. For the dark side looks back. Nature surrounds us and binds us. Help it we must. Neglect and indifference to nature leads to the dark side.

Why Is The Monarch Butterfly Population Shrinking?

Margaret Roach, reporting for Latina Lista:


“Where are the monarch butterflies this year?” One of many recent emails on the topic asked me. Headlines about monarch decline seem to confirm gardeners’ observations: Populations of the once-familiar orange-and-black creatures are not what they were. What’s going on, and how bad is it? Is there anything we can do?

Some good links to other information on Monarch Butterflies at end of article.