The latest yearly count of the monarch butterfly shows a dramatic increase in their numbers, partly reversing at least temporarily recent sharp declines. Scientists with World Wildlife Fund Mexico estimate that some 56.5 million monarchs gathered for the winter after their trek across the United States—up more than 60 percent from last year, when 34 million were counted in Mexico’s Sierra Madre.
While the rebound is heartening, the overall picture is still not good, as the rebound came from very low levels, and remains well below the numbers over the past 21 years. Butterfly migration counts in Mexico, their primary winter resting place, have only been kept since 1994.
The modestly better news came out shortly before the National Resources Defense Council turned its guns on the Environmental Protection Agency, claiming it has failed to heed the NRDC’s warnings, contained in a petition filed more than a year ago, about the dangers to monarchs posed by glyphosate. The NRDC filed the suit in U.S. District Court in New York. The advocacy group and numerous other organizations have pointed to the correlation of the butterfly population decline with the increased use of glyphosate, which is a very mild herbicide introduced decades ago (well before GM crops) to replace far more toxic chemicals. They often release charts such as this:
According to the NRDC news release:
“The longer EPA delays, the greater the risk we could lose the monarch migration,” Sylvia Fallon, an NRDC senior scientist and director of its Wildlife Conservation Project. … Experts say the primary cause for the population collapse is the skyrocketing use of the herbicide glyphosate (originally marketed as Roundup) on genetically modified corn and soybeans, which has wiped out much of the milkweed — a native wildflower — that monarchs need to survive. Since EPA last reviewed the safety of glyphosate in 1993, its use has increased ten-fold, yet the agency has never considered the herbicide’s impact on monarchs.
In effect, the NRDC is accusing the government of conspiring to suppress evidence that the popular herbicide, often paired with GMO crops, is responsible for killing off the monarch butterfly population. Other activist groups have used the same data to mount an offensive against all GMO crops.
“Monarch butterfly decline being caused by GMO agriculture,” blared a recent headline in NaturalNews.com, a junk science site that sells often bogus alternative health remedies, yet enjoys enormous popularity and even credibility among mainstream anti-GMO campaigners.
Does the science stand with the NRDC’s lawsuit and its claims?
Although more reliable statistics are only available for the past two decades, experts contest the simplistic narrative that the monarch butterfly population is mortally threatened.
“Monarchs are not in danger of extinction,” said Lincoln Brower, a monarch conservation scientist at Sweet Briar College. “What is endangered is their spectacular migration and overwintering behavior.”
What is not widely understood is that scientists measure the overwinter numbers in Mexico, not the numbers of monarchs. The situation, and the longterm trends, are not good, but even if the current declines continue, the monarch and other butterflies are not headed toward extinction.
Experts outside of the “activist circuit” believe the monarch butterfly population’s overwintering habitats have been in decline for decades, pre-dating both the widespread of glyphosate in agriculture in the 1980s and the use of GM crops in the mid-1990s.
The decline in butterfly populations, while extremely concerning, is also not unique to the United States. It mirrors almost exactly what is occurring in other places around the world, most especially in Europe, where the growing of GMOs is almost totally nonexistent.
Scientists do know that certain herbicides kill the nuisance milkweed–the most common butterfly habitat in the United States. That’s certainly a contributing factor in altering migratory behavior. But how much, considering that glyphosate use has not accelerated in other places in the world where butterfly populations are in steep decline?
The largest factor in the decline is almost certainly the declining amount of productive agricultural land, in Europe and the United States in particular. Less milkweed—a bane of farmers—grows when there is less farm acreage. The reality is the land use for agriculture is going down while land not suitable for monarchs and other butterflies is going up. According to the USDA, land area designated as “Non-Agricultural”, mainly “Forest land” and “Special Uses”–rural parks, wilderness areas and rural transportation—has been increasing. The proportion of the land base in agricultural uses declined from 63 percent in 1949 to 51 percent in 2007, the latest year for which data are available.
A 2012 study in the journal Insect Conservation and Diversity estimated that between 1990 and 2010, milkweed prevalence declined 58 percent in Midwest agricultural areas where farmable acreage shrunk dramatically. Over the same time frame, the monarch population declined 81 percent. Additionally, according to Chip Taylor, director of Monarch Watch and a professor of ecology at the University of Kansas, a 2007 congressional ethanol mandate increased the price of corn and soybeans, which encouraged farmers to convert grassland–where milkweed grows–into cropland.
What role then does glyphosate play?
The on the ground reality is certainly more complex than NRDC’s simplistic narrative. Corn and soybeans are the two biggest crops in the US, amounting to ~170 million acres. Cotton is about 10 million acres. This graph shows the adoption of herbicide resistant (HT) crops and crops that are engineered to generate a pesticide found commonly in nature (BT).
It is important to note that BT crops only affect insect pests that are susceptible (mostly the larva of some moths and butterflies and a few beetles) and that take a bite out of the plant. Because Bt isn’t expressed in the pollen, it doesn’t affect winged pollinators. Other insects, plants and animals are completely unaffected by the Bt protein (one of those pesticides that are used widely by organic growers), although if they eat enough it will give them a nutritional boost.
Now compare those trends to the population studies on monarch overwintering populations in Mexico:
As you can see, the population crashed during the winter of 1997–when a fraction of the herbicide tolerant crops were being used relative to today. The overwintering numbers also increased dramatically at the turn of the century just as Ht crop usage and the use of glyphosate soared.
About caterpillars and butterflies
The issue with monarchs is complicated by the fact that as caterpillars they can eat only one food, the milkweed plant. Still monarchs thrived as our field crops increased, because the milkweed they rely on could survive tilling (the previous normal method of weed control), such that when its tap root was cut by tilling, often the large pieces healed themselves and the plant still came up in the spring. Milkweed was in fact fairly common in corn, cotton and soybean fields. So the larger population of monarchs we saw in the early 90s was largely because of the way we weeded our field crops.
Then GMO corn, cotton and soy were introduced that were resistant to glyphosate and many farmers quit tilling to control weeds and went to spraying glyphosate instead. Milkweed is not immune to glyphosate though and the amount of it in Midwest corn and soybean fields has gone down. But given all the land that is not farm land, that alone wouldn’t account for their decline. Indeed, Andrew Kniss, a weed expert at the University of Wyoming, wrote in a blog post that the use of herbicide-tolerant plants glyphosate has had only a limited impact on native plant diversity outside the border of the agricultural field. So to understand the problem, one has to understand the insect itself.
The monarch spends the spring and summer in most of North America, and while in North America the monarchs will go through up to seven generations. Each generation lasts from 6 to 12 weeks, depending on climate and food supply. The butterfly form itself normally lives from two to six weeks.
As monarchs migrate north, the female lays her eggs only on milkweed plants. The eggs take about a week to hatch into larvae (caterpillars). The larvae feed on the milkweed for about two weeks and then they attach themselves to a twig, shed their outer skin and change into a chrysalis. In about two weeks a full-grown monarch breaks free to start the next generation. Some of each new generation moves north with the warming spring weather. Note that while the caterpillars only live on milkweed, the adult form is free to sip nectar from any flowering plant they find.
As fall approaches a somewhat unique version of the monarch appears. Unlike their parents before them, they don’t immediately reproduce but instead falling temperatures make them avoid procreation and begin the migration back south. Depending on where they begin this trip, these last of the season monarchs will travel many hundreds or even thousands of miles to their winter grounds, mostly in Mexico (East of the Rockies, they will winter in Southern California, and there are a few populations of monarchs living year round in Southern Florida, California and Texas that don’t migrate at all).
On their way South, they store fat in their abdomens as it is needed for the long flights and to last through their winter hibernation, which lasts from November till about May. When they arrive in Mexico, the monarchs gather into dense clusters in the branches of the trees, and by late winter these clusters will contain hundreds to thousands of them. During their long hibernation they will remain perfectly still, clustered in these Mexican forests, surviving only off of their stored fat reserves.
As warm weather arrives in Mexico in February, they begin to move again and during the day the monarchs will once again begin to gather nectar. Ultimately they will mate and lay eggs as it is only their plump offspring which will make the return migration back to North America.
This complex life cycle shows why the key to their survival is multifaceted. Indeed, probably the most important need these insects have is the amount of nectar providing plants they can use to develop the reserves that are needed to make it through their long migration and hibernation period.
Finally there is also the pressure from the dwindling forest area in Mexico where much of their population over winters. The deforestation stems from illegal logging in Mexico. According to Politifact, which reviewed this controversy, it has reduced the areas where monarchs can migrate, affecting their lifecycle. A new study of the monarch butterflies’ winter nesting grounds in central Mexico showed that small-scale logging is worse than previously thought. The reserve’s fairly small 33,482-acre core zone lost 41 acres of pine and fir trees so far in 2013, about half of that because of illegal logging while the rest of the loss was due to drought or disease-control removal of trees.
Mexico’s government had begun to protect the Monarch’s over-wintering grounds in recent years and in 2012 aerial photographs found very little deforestation due to logging over the previous year (at its peak in 2005, logging depleted as many as 1,140 acres each year).
Still this new study’s analysis of photos taken a decade apart showed that small-scale logging has never gone away and while it is not seen in year-to-year comparisons, the study found the losses by comparing 2001 photographs to the recent ones taken in 2011.
Given the multi-faceted nature of the problem, it seems clear that there are many factors causing the decline, and so the solution also has to address all of these factors. Indeed, many people are now coming to their aid by planting the flowering plants and milkweed they need to survive. Here is a chart of success stories–the creating of new monarch butterfly habitats.
While the total solution is not clear, words of caution, as many ecological conscious home gardeners have started planting milkweed in an attempt to help the monarchs. Caterpillars eat the weed because chemicals within the plant make them unpalatable to predators–but this same latex rich sap is also toxic to people and quite capable of causing severe eye injury, up to and including blindness if you get the sap in your eyes.
So if you do decide to plant it, don’t put it where kids can kids play in it and handle it carefully.
Arthur Doucette is a retired software developer, now writing about issues involving Genetic Engineering.