Over several years, the media have been warning home gardeners that a favorite butterfly, the monarch (Danaus plexippus), is in serious decline. Apparently, it might even face extinction if something isn’t done to help it. Various factors are involved, including:
- Deforestation of wintering forests in Mexico;
- Disruptions to their migration caused by climate change;
- Use of insecticides on crops, resulting in the unintentional poisoning of passing monarchs;
- Decrease in the milkweed (Asclepias spp.) population, the only food source of monarch larvae, along their migratory corridors.
For example, as agricultural practices intensify and even marginal land is absorbed into farmers’ fields, this leaves less space for milkweeds to grow. Plus, milkweeds are seen as weeds by farmers and, and herbicides continue to be used to control their numbers when they show up in agriculture fields. Thus, monarchs would appear to be facing the loss of a vital source of nourishment.
As a result of these and other factors, media have been promoting the idea of growing milkweeds in home gardens to replace the environment of the fields where it used to grow.
Such a Fascinating Subject
I’ve written about the predicament of monarch butterflies several times over the years in this blog, including in the following articles: Fresh News About Monarch Butterflies, Monarch Butterflies Are Back!, Plant More than Milkweed to Save Monarchs and Monarchs Arrive in Europe!
I confess to being a serious monarch lover myself, having raised and studied them as a child by moving wild caterpillars to milkweed plants I grew in my own backyard just for that purpose.
And monarchs are certainly worth saving should it turn out they need help. They’re large, very colorful, attractive butterflies with black-veined orange wings and black bodies with white spots. Every year they travel from their winter haven in the mountains of central Mexico and California to their summer haunts throughout the United States and into southern Canada, a distance of some 3,000 miles (4,800 km) in some cases. Their migratory pattern is the most highly evolved of any known butterfly.
News This Year Is Excellent!
But the news about monarch butterflies isn’t all doom and gloom. In fact, some recent reports about monarchs are positively rosy! Here are two reports for 2022 that suggest the monarch is actually doing quite well, thank you.
Butterflies Thrive in North America
The report is entitled Monarch butterfly populations are thriving in North America. It comes from research at the University of Georgia published in Global Change Biology. It suggests that, while there may be some decrease in population in winter colonies, this is more than compensated by population growth during the summer. Andy Davis, corresponding author of the study and an assistant research scientist in UGA’s Odum School of Ecology, points out. “There’s this perception out there that monarch populations are in dire trouble. But we found that’s not at all the case. It goes against what everyone thinks, but we found that they’re doing quite well. In fact, monarchs are actually one of the most widespread butterflies in North America.”
The study compiled 135,000 monarch observations between 1993 and 2018. They came from the North American Butterfly Association’s annual butterfly count. It covers the the entire breeding range in eastern and western North America. There has been a decline at some sites. This is particularly the case in the US Northeast and parts of the Midwest. However, numbers in other areas, notably the US Southeast and Northwest, haven’t changed or are even increasing. The result is a slightly positive overall trend across the species’ range.
Among factors that appear to be helping are annual temperatures. They have generally been beneficial to monarchs. And they help to compensate for the negative impacts of using the herbicide glyphosate. Plus, its agricultural use appears to be leveling off. Also, the butterflies seem to breed in greater numbers when fewer of them arrive in their summer habitat. Called density-dependent reproductive compensation, this offsets the effects on mortality and reproduction.
Still, the report cautions against complacency, suggesting accelerating climate change may bring growing threats. In addition, it’s possible that the increases of summer monarchs in some regions may reflect replacement of migratory populations with resident ones. This might be specially the case in California and in the South.
However, the report is reassuring in that they are not finding any sign of ubiquitous downward trends in summer monarch abundance.
And Now, News From Central Mexico. . .
Monarch butterfly numbers in Mexico rise by 35% Mexican experts said in May 2022 that 35% more monarch butterflies arrived this year to spend the winter in mountaintop forests, compared to the previous season. Experts say the rise may reflect the butterflies’ ability to adapt to more extreme bouts of heat or drought by varying the date when they leave Mexico.
The government commission for natural protected areas said the butterflies’ population covered 2.84 ha (7 acres) this year, compared to 2.1 ha (5.2 acres) last year.
The annual butterfly count doesn’t calculate the individual number of butterflies. Intead, it uses the number of acres they cover when they clump together on tree boughs.
Each year the monarchs return to the United States and Canada on an annual migration. Loss of the milkweed plants they feed on north of the border and deforestation in the butterfly reserves in Mexico threatens this migration.
Gloria Tavera, the regional director of Mexico’s Commission for National Protected Areas, said logging in the butterflies’ wintering ground rose by about 4.5% this year, to 13.9 ha (34 acres). However, fewer trees were lost to fire, drought or plant diseases and pests. So overall tree loss in the 2021-22 season was about 18.8 ha (46 acres), down from 20.6 ha (51 acres) in the 2020-21 season.
A Great Source of Information on Gardening Science
I would like to thank Rebecca Last-Guenette for the above information, which came from her excellent Gardening Science Newsletter that I receive monthly. Maybe you should sign up too! You can do receive it by contacting her at email@example.com. And it’s free!