TUPPER LAKE - Lincoln Brower has spent decades studying the monarch butterfly, a species that has been on the decline in recent years. On Thursday, June 26 at The Wild Center, Brower gave an overview of biology of the butterfly and the threats that it is facing.
A professor at Sweet Briar College in Virginia, Brower first began studying butterfly biology in 1954 when he was a graduate student at Yale University. He has since written or co-written more than 200 scientific papers on the subject. He was inspired to study monarchs after visiting their overwintering site in central Mexico in the late 1970s.
The monarch population, which was once in the hundreds of millions or perhaps billions, is now at the point where one severe winter could knock the population down to the point where the migration could end, Brower told the Lake Placid News. If the migration ended, monarchs would no longer venture north to the Adirondacks from Mexico.
Mike Lynch/Lake Placid News
Monarch butterfly population numbers are decreasing in the Adirondacks.
"Everyone is familiar with endangered species where the species is threatened with extinction," Brower said. "The monarch is not threatened with extinction, but it has the most marvelous migratory and overwintering behavior of any butterfly on the planet, and both of those aspects of its biology are threatened with extinction because of what's been happening in Mexico and because of what is happening in the United States."
In Mexico, the government has stopped the large-scale illegal logging where the monarchs overwinter, but small-scale logging still takes place there, cutting holes in the protective layer at the top of the forest, he said.
"The forest is an umbrella and a blanket that protects the butterflies from winter storms, which periodically occur and are devastating to the butterflies," he said.
Brower also said that ecotourism is hurting the butterfly in some places because of the large crowds that visit the forests where the butterflies live.
In the United States, the monarch is being affected by the declining amount of milkweed plants in the Midwest, where farmers are treating fields with glyphosate, an herbicide that kills milkweed and other plants. The farmers' crops of soybeans and corn are genetically modified plants that are made to be resistant to glyphosate. The monarch butterflies rely on milkweed as a main food source, which also provides them with a toxin that makes them unattractive to predators such as birds.
"Why do monarchs migrate into the temperate zone? They are tropical butterflies like all their ancestors. Well, the answer is milkweeds," said Brower.
Brower said that scientists believe that monarchs followed the milkweed north as part of their evolution. "In order to exploit (the food source), they had to migrate north in the spring after freezing weather, then back in the fall, because the plants were gone after the first frost occurred," he said.
In addition, monarch butterflies only lay their eggs on milkweed leaves and their caterpillars eat only milkweed. About two weeks after a female butterfly deposits her egg on the under side of a milkweed leaf, the caterpillar which hatched from it forms a chrysalis on nearby plant material, and about 12 days later a new butterfly emerges.
In the fall, monarchs hatch in the Adirondacks, live up to nine months and make a journey to Mexico, where they winter in fir forests in high-altitude mountain areas.
The following spring, the monarchs mate and head northward, stopping first in the southwestern U.S. where they lay eggs on milkweed and die. A new generation is born and continues north. Each of these north-bound generations lives six to eight weeks. It takes three to four generations for monarchs to reach the Adirondacks. The last generation born in the north is called the migrating generation because it lives much longer, making the entire trip in the fall to Mexico, wintering there, and flying back to the southern U.S.