Tuesday, August 17, 2010

On killing monarch butterflies

I killed two monarch butterflies last week. I certainly didn't mean to, and felt bad the moment I did. Fortunately my daughter, who has several children's books describing the wonder that is the monarch's unusual life cycle and epic migrations, did not notice or she would have been horrified. For those who did not learn and internalize their monarch butterfly facts as children, here are some salient points about their remarkable lives:

- the monarch lays its eggs on milkweed plants, which can be toxic to many animals. The caterpillars accumulate the toxins in their tissues, rendering the insect unpalatable to birds. The caterpillars and the butterflies advertise this fact through bright coloration.
- monarch butterflies born east of the Rocky Mountains undertake an annual north-south migration between southern Canada and an upland region in Central Mexico
- the migration takes longer than the lifespan of any individual butterfly. The adult butterflies lay eggs as they go along, with each successive generation of butterflies continuing onward to the correct destination (how each butterfly knows where to go is not known)
- in their Mexican wintering grounds the monarchs congregate in enormous numbers on coniferous trees, much the way bats cluster in huge numbers in many caves (click here to see an image)

It's consequently not surprising that many people young and old feel much more passionately about monarch butterflies than they do about most other insect species. It is also therefore not surprising that the monarch's geographically confined Mexican wintering grounds were made a biosphere reserve so as to protect that important habitat from forest clearance. Nonetheless, illegal logging does take place in and around the reserve, something conservationist groups have for several years been pressuring the Mexican government to control, with some success. Even so, the number of monarchs in Mexico in recent winters has been falling.

In Ontario and Quebec, monarch habitat is largely dictated by the availability and distribution of milkweed, a field/meadow plant. And in those two provinces (and Manitoba as well), milkweed plants have long been listed as noxious weeds to be controlled. As mentioned above, many species of milkweed plants (genus Asclepias) are toxic, and so domesticated grazing animals that consume them in large quantities, especially sheep, can become sick or even die. Of course, grazing animals can ordinarily recognize common toxic plants and therefore avoid them, as they do with milkweeds, unless there is nothing else available to eat. So it is that to protect sheep milkweed is officially designated a noxious weed which, if it is found present on your property, you are supposed to destroy pursuant to Ontario's Weed Control Act. It does not matter whether you or your neighbours actually have any starving sheep on your land - you're supposed to get rid of milkweed.

Fortunately for monarchs, most people don't recognize milkweed plants let alone know they have a duty to destroy them, and even those who are aware of these facts and have milkweed on their land usually don't actively target them. However, common farming practices used to produce corn and soybeans - the most common field crops in Ontario - and many other crops involve the application of herbicides that control all weeds, including milkweed. Moreover, milkweed also tends not to grow in well-grazed pastures. The result is that in Ontario's countryside you're most likely to find milkweed plants congregated along roadside ditches and other areas around the margins of farmland.

And that's how the two monarchs I mentioned earlier met their end on my car windshield as I drove along a country road in Prince Edward County. The reality is that southern Ontario's best monarch habitat coincides with Ontario's road network. Who knows how many monarchs die in collisions with cars in Ontario each year; I'm willing to bet in Prince Edward County alone several hundred die this way each day in August. Funny how the children's books don't mention this fact.

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