The population of the beloved monarch butterfly has seen a radical decline in the last decade—a trend that, unless something is done, shows no sign of lessening. While there are several contributing factors, chief among them, according to the Center for Food Safety, is the widespread use of Monsanto’s Roundup herbicide, which, as it turns out, kills off the monarch’s chief source of nutrition. It is a situation that has put environmentalists—as well as lovers of this incredibly delicate and beautiful species—on high alert.

The Food Source

“At least half of the monarch population breeds in the Midwest, in the Corn Belt,” Bill Freese, Science Policy Analyst for the Center for Food Safety (CFS), explained to Organic Connections. “They mate, they lay eggs, and then they have their larva that feed on milkweed plants. They are completely dependent on milkweed; it’s the only host plant that will support the monarch caterpillars. The caterpillars will feed on the milkweed plant and then they’ll pupate and become butterflies.

“The butterflies then migrate all the way to the mountains of northern Mexico, where they overwinter in a very, very small and confined area.”

Eradication of Milkweed

“There are various causes for the monarch decline; it’s not one thing,” Freese continued. “People focus on the factor of illegal logging that’s taking place in protected forests in Mexico where the butterflies overwinter. However, in the last few years Mexico has really clamped down on that, so it’s much less of an issue now.

“More and more entomologists are seeing a crash in the population of milkweed in the Midwest as the major cause of monarch decline. In 1999 a group of scientists did a very, very careful survey throughout the state of Iowa to see how much milkweed was in the state. They looked at all different habitats—corn and soybean fields as well as conservation reserve land, pastures and on roadsides, because you find milkweed on roadsides. They established how much milkweed there was, and then came back a decade later and did the same thing.

“In that 1999 survey, most milkweed was found in corn and soybean fields. Milkweed is really well adapted to survive in agricultural fields; it has very deep roots and is a perennial plant. In 2009 when they did the second survey, they found that milkweed in agricultural fields had almost been decimated. There’s very, very little of it left.”

Where Did It Go?

To understand what has killed off milkweed in such high quantities, it is important to understand the radical rise in the use of Monsanto’s Roundup herbicide, which occurred at the same time.

The beginning of the story is with the genetic modification of crops to make them “Roundup ready”—some of the very first genetically modified organisms (GMOs). Because they were so modified, farmers could spray Roundup herbicide onto these crops without harming them.

“Roundup Ready crops were introduced in 1996,” Freese related. “In 1999, when that first survey was done, this practice was still just getting started. Prior to the advent of Roundup Ready crops, very little glyphosate [Roundup’s active ingredient] was used in the Midwest. That is because glyphosate is very toxic to plants, to crops—corn and soybeans; you can’t spray it.

“With the advent of Roundup Ready crops, there was about a tenfold increase in glyphosate use. It is sprayed in the spring and early summer as crops are beginning to come up, to kill weeds as they start growing, since it won’t harm the Roundup Ready crops. It turns out that spraying Roundup at that time is the perfect time to kill milkweed. Milkweed is most susceptible to glyphosate in the late spring and early summer. It’s very clear that this huge decline in milkweed is due to this huge use of Roundup.”

As a side note, milkweed poses no threat to crops at all, except in a very few isolated instances.