Monarch Butterflies – against all odds

by Lorraine Julien

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Recently, I’ve noticed some disturbing articles in several southern Ontario newspapers and on the internet reporting that Monarch butterflies may be facing another year of declining numbers in their struggle against loss of habitat and North American weather extremes. These migratory insects spend their winters in Mexico where the population count this past winter was the lowest on record.

According to a recent Globe & Mail article, the largest Monarch populations are found in southern Ontario and Quebec although they do range across all of North America. The Monarchs that migrate south from central and eastern Canada in the fall (called the “Methuselah” generation), are long lived insects that travel up to 2500 km to several points in Mexico where they winter in dense, tree-covering colonies first discovered by scientists in the 1970’s. They begin their northward trek each spring to certain areas in Texas where they breed, producing offspring that eventually return to Canada each summer to repeat the cycle. A single butterfly does not make the entire migration – it takes three or four generations before they reach Canada. Probably no other insect, among the millions of species on earth, performs a similar migration.

The downward population trend has been studied for a number of years by university researchers and conservation groups. The main factor for the decline in 2009 was the extremes in temperature – for example, spring temperatures in Texas were very high last year which depleted some of the migrants as they headed north. Then those Monarchs that did manage to arrive here were greeted by a cold, wet summer. Extreme weather in one area would have been bad enough but it’s very rare they’d encounter extreme weather all across their North American migratory routes.

Although weather can really affect Monarch numbers, they’ve also suffered from a lack of habitat:

• Massive expansion in the amount of genetically modified corn and soybean crops have led to an increase in herbicide use which has eliminated the milkweed plants that Monarch larvae depend on for food

• Rural land is rapidly being developed for housing and other development

• Weeds are either cut or sprayed alongside many highways effectively eliminating milkweeds

The Monarch has proved itself to be a highly adaptive species, though in the last 150 years there has been a major shift in the North American distribution of the eastern population. This appears to have resulted from the widespread conversion of the natural mid-western prairie to cropland, a process that destroyed much of the native prairie plants and animals including many species of milkweeds. At the same time, considerable areas of the deciduous forests of eastern North America were cleared for farming, allowing the rapid spread and increasing abundance of the common milkweed in the cleared lands. The cleared portions of the eastern deciduous forests correspond to the main breeding area of the eastern population of the Monarch today.
Monarchs are not in danger of extinction but their ability to migrate successfully is a real concern. Human activity does not seem to bother them – they just fly around doing their own thing! These beautiful creatures will seek out even small patches of milkweed and will lay their eggs as long as the plants are healthy.

We can all do our part by letting milkweeds grow wherever possible. I noticed some milkweeds popping up in my garden this year but, instead of pulling them out, I’ve let them grow alongside the flowers and will see whether I have any Monarch visitors this summer. I’ve also noticed milkweeds regenerating in nearby fields that have been left dormant for a few years and have gone back to a natural state.

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Please feel free to report any observations to Lorraine Julien at naturewatching@gmail.com  or Steve Blight at natureobservations@rogers.com