I recently heard a talk about monarch butterflies that left me in awe, once again, of nature. These remarkable insects have been in the news because of declining numbers—largely because of global warming, it seems. We’ve only begun, however, to learn how remarkable they are, even with the head-of-a-pin-sized brains. You might wonder why I’m discussing butterflies in November, but it’s not the first time I’ve done that. Besides, global warming has made it relevant. So what about monarchs? Perhaps the most remarkable thing is that they migrate. And to do so it takes about four generations. This deeply embedded behavior shows an intelligence in nature that we’re reluctant to grant. Still it’s clearly there. I live in Pennsylvania and we have monarchs around here and they can be found as far north as southern Canada.
Photo credit: Kenneth Dwain Harrelson, via Wikimedia Commons, GNU Free Documentation License
These monarchs around here aren’t the ones who left their overwintering spot in Mexico. The earliest ones we see up here may have flown in from the Carolinas or the Midwest, where they may’ve been born. As adults they feed on flower nectar, but to be born they require milkweed plants. Monarchs only lay their eggs on this one plant family. The milkweed contains a toxin that they’ve evolved to eat and that toxin gives them a really bad flavor. That’s why birds tend not to eat monarchs. So they reproduce in northern locations until environmental cues change the late season eggs. These late season generation produces the butterflies that will migrate. Instead of hanging around sipping nectar, they find south (they can tell time and they only fly on days with a south wind) and make their way to one specific area in Mexico to overwinter. They don’t eat at that stage.
In the spring, hungry, they following blooming desert flowers north. They follow the food supply, birthing new generations to carry on, until they reach the latitude they prefer. So some stay around here, eating and reproducing until the cycle begins again in the autumn. It might seem like a lot of extra work (consider what we do in the office all day and try to criticize) yet it demonstrates the remarkable intelligence of nature. That migrating generation has to know to fly south and they have to be able to find direction. Once there, and ready to return, their offspring’s offspring will (we suspect because of other species) know where their great-great-grandparents lived and they head there over three generations. All of this is being endangered by global warming, however. Because one species thinks of itself alone as remarkable.
