The monarch butterfly population is at its lowest this year.

The 2013 Mexico overwintering population of monarchs was found to be 0.67 hectares of fir forest, said John Pleasants, adjunct assistant professor of biology.

This has been the lowest count since population size was recorded in 1994, and the population is down half of what it was last year.

Since 1999, the size of the overwintering population has declined by 82 percent, said Pleasants. This year’s data is estimated to include 44 million butterflies compared to the high of 1.4 billion in 1996.

Nathan Brockman, butterfly wing curator at Reiman Gardens, said there are multiple factors that have led to the decrease in butterfly population. In the Midwest, there has been a loss of habitat, as well as a loss of milkweed, a monarch’s source of food, due to pesticide exposure.

Milkweed is a host plant for monarchs, meaning females look for milkweeds to lay their eggs. Larvae only eat milkweed. 

Brockman said weather has a huge factor on butterfly populations as a whole.

In droughts, the milkweed does not survive. Neither cold nor wet springs are good for butterflies. If the milkweed doesn’t grow, monarchs don’t lay eggs.

Robert Hartzler, professor of agronomy, started to notice that milkweed plants in corn and soybean fields were decreasing. In 1999, he did a survey across Iowa and found 50 percent of the fields had milkweeds in them. In 2009, he completed the same survey and found eight percent had milkweed.

There have been a few concerns with crops affecting milkweed populations. There was concern that the pollen from Bt corn, a genetically modified corn, would fall on milkweeds and poison the monarch larvae. Hartzler said the data shows there weren’t sufficient amounts of toxin to be a concern.

Hartzler also looked at pesticides being an issue. Roundup Ready is a pesticide that kills milkweeds. Farmers are using Roundup-resistant crops, allowing them to use the pesticide. Farmers don’t intentionally kill milkweeds, they’re “just innocent bystanders,” said Hartzler.

Hartzler found “higher concentrations of milkweed in the road ditches than in the fields.” However, monarchs won’t lay their eggs in the ditches, leaving room for solutions.

Brockman said “there’s not one easy answer” to how people can help the monarchs. A way that people can help monarch populations is to plant milkweed.

One way is “having more natural spaces,” said Brockman.  Butterflies are able to thrive in these areas. 

Pleasants said the Conservation Reserve Program could reserve land for milkweeds. The government pays farmers not to plant land through the Conservation Reserve Program.

As for the monarchs, it is uncertain as to what will happen with the decreasing populations. Pleasants said he has concerns on whether or not the monarch population will be able to bounce back because they are vulnerable with low numbers.

“Monarchs are the butterfly chosen for classrooms,” Brockman said.

He also said monarchs are what people think of when they think of their favorite butterfly.