Monarch's long migration is a generational tale

When I was 12 years old, many years ago, I collected butterflies. That required a killing jar. A drugstore in downtown Robbinsdale, four blocks from our house, sold me the essential ingredient: chloroform, several ounces in a tin bottle.

I needed a sprinkle of chloroform on a dab of cotton in a fruit jar. With that, my net, and a handful of cookies I would ride my bike into the wilds of New Hope. It was mostly empty land, farmed, or gone to weeds and wildflowers.

That is where I hunted, my prey to meet their end in the jar.

I'm certain that monarchs were trophies of my hunt. Monarch butterflies are a worldwide species, with a 65-million-year history. A worthy trophy.

History was flipped in early September when I became babysitter for three monarch caterpillars and 42 monarch chrysalises (not cocoons), all in a large screened box. I was charged with their care by three grandchildren, the collectors. The kids were going to the lake.

I watched 10 butterflies emerge from chrysalises during the time I babysat.

They appear folded like card tables. Wings and legs are tight to a bulbous torso. Wings and legs extend as the butterfly hangs on the shreds of its cradle. The torso lengthens. Fluid is pumped through special veins to stiffen wings.

The kids did their collecting in a spread of marsh milkweed surrounding a pond near their Plymouth home. They wanted to save the caterpillars from the usual heavy predation. They wanted to beat the odds by setting to wing 100 percent of their hatch.

Most North American monarchs winter in Mexico. The butterflies I watched are on their way to Mexico right now. They will arrive in early November.

In mid-February, these monarchs begin the return trip north. Individuals get as far as Texas. They mate, lay eggs and die.

The eggs hatch, caterpillars grow, enter the chrysalis stage, then emerge as butterflies. This second generation flies to Minnesota. Here, two or three more generations are produced. The last generation brings us again to the Mexico departure.

Genetics program the early generations in this sequence to die after several weeks. Shorter days, cooler weather, seasonal change of milkweed plants trip a genetic switch that preps the autumn butterfly for its long journey, and a life of six to seven months.

Science does not know for certain, but theory is that the butterfly's eye contains a sensor that tracks the movement of the sun, adjusting for geographic position. The antennae of the monarch are believed to be sensitive to the Earth's magnetic field.

This information guides the butterfly along its genetic map, both south and north. (And you think your iPhone is good.)

The monarch does not spin its chrysalis, as some creatures spin a cocoon. The monarch becomes the chrysalis. It is a transformation, caterpillar to butterfly, a thorough and dramatic change in form and appearance.

The monarch's place in the world is no different from that of so many bird species. Loss of habitat and extensive use of herbicides have dramatically reduced the number of milkweed plants, the food plant for this butterfly's larvae. This has reduced monarch numbers by millions.

Capturing caterpillars to be released as butterflies is best done as an educational experience. To save the monarch, it is far better to plant native milkweed, to support less use of herbicides and to work for habitat preservation.

Much information is available at monarchwatch.org.

Lifelong birder Jim Williams can be reached at woodduck38@gmail.com. Join his conversation about birds at startribune.com/wingnut.