Missing milkweed

“We’re seeing a tremendous decrease in available habitat in the American Midwest,” says Chip Taylor, a professor of insect ecology at the University of Kansas. Corn and soybean crops, increasingly grown for biofuel, have dramatically reduced milkweed — the plant that caterpillar-stage monarchs rely on exclusively — and other habitat.

Climate conundrum

Monarchs cannot survive cold temperatures — they must migrate to warmer climes. The impacts of climate change on wintering monarchs could go either way, says University of Guelph researcher Ryan Norris. “Long-term warming would be good, but if climate change means an increase in the number of catastrophic events, that would be bad.”

First generation

During the spring migration north, monarchs lay eggs on milkweed in the southern U.S. before dying. Those offspring complete the northward journey. Weather plays a key role in the process. Lots of moisture and cold temperatures can cause monarchs to freeze to death, and a late spring can delay milkweed growth, leaving no suitable place to lay eggs.

Exotic threat

Is dog-strangling vine, an invasive species that resembles some native milkweed but cannot support caterpillars, affecting monarch populations? Monarchs have been observed laying eggs on the look-alike exotic, but as the University of Kansas’s Taylor says, “there’s still a lot to learn” before scientists can accurately assess the threat.

Butterfly gardens

Taylor insists the best antidote to big agriculture is small-scale gardens of native plants, which provide refuges for pollinator species such as monarchs in urban and rural backyards. “Seventy per cent of plants rely on insect pollination,” he says. “We’re losing sight of how everything is connected.”

On point

During the September migration, Parks Canada interpreter Sarah Rupert has witnessed up to 500,000 southbound monarchs roosting in trees in Ontario’s Point Pelee National Park, which juts into Lake Erie and forms a natural conduit. Parks Canada is restoring savannah habitat to make Point Pelee more attractive to butterflies throughout the summer.