(Chelsea Update would like to thank Tom Hodgson and the Waterloo Natural History Association for the photos and information in this story.)
Some local residents may have noticed that monarch butterflies have not been visiting their flower gardens this summer, and for good reason. Monarchs have been almost entirely absent from Michigan and other northern breeding states this year.
These butterfly populations periodically go through low cycles, but they have been on a rather steep decline in recent years. The numbers of these orange-and-black butterflies on their wintering grounds in the mountains of Mexico was down 59 percent from the previous year, and was the lowest recorded since records have been kept. This represents one-fifteenth of the number counted in 1997.
So, what’s happening?
The World Wildlife Fund, one of the groups sponsoring the international monarch butterfly census, reports that that there are a number of factors at play. Illegal harvesting of trees on the winter roosting sites, the increase in global temperatures and changing agricultural practices have all played a part. The first threat, illegal logging on their wintering grounds has been largely stemmed and these sites are now stable.
That leaves the changing climate and agricultural practices. Summer heat waves experienced in the U.S. in recent years have included temperatures hot enough to kill developing monarch eggs. Bouts of increasingly severe weather along the monarch’s spring migration routes have also caused an increase in adult mortality. The same weather events have also disrupted migration flights, delaying the monarch’s arrival in northern breeding areas like Michigan and sometimes preventing them from reaching these destinations at all.
Finally, the development of “Round-up resistant” corn and soybeans has allowed farmers to treat fields of these crops with Round-up to kill off unwanted plants like milkweed, which is the primary food source for monarch larvae.
Historically, the equivalent of thousands of acres of milkweed grew as scattered volunteers in corn and soybean fields throughout the country. Now milkweed has been largely eliminated from these sites. What is left of the milkweed population is largely confined to roadside ditches and waste areas. If the larval food source continues to decline, so will the monarch population.
Each summer for the past 20 years, volunteers from the Waterloo Natural History Association have collected monarch eggs for a living life cycle exhibit at the Discovery Center. The exhibit is usually in operation from July through mid-September. This year, not a single egg was found until this past week.
The center now has enough eggs and young larvae to start the exhibit by this weekend and the exhibit will eventually include all stages of the monarch’s life cycle.
Visitors will be able to see larvae in various stages of growth as well as monarch chrysalids, and emerging adults. The larvae are raised in a protected environment free from predators and parasites so that survival is nearly 100 percent.
The adults are released each day so that they may begin their flight to Mexico for the winter. Sadly, if the monarch populations continue to crash, this may be one of the last years for this exhibit.