Every Fall we watch the Monarch Butterfly pass through our Communities. All heading in the same direction: East to West. For me it's a harbinger of summer's end. Where are they coming from? Where are they heading?

(The male Monarch Butterfly is easily distinguished from the female through the two highly visible black spots on the male's hind wings and the thinner black webbing within the wings. The female's webbing is thicker and she has no identifying wing spot as the male does. )

Did you Know?

* The longest recorded flight of a monarch butterfly is more than 3,000 miles. The monarch can cover 80 miles a day when migrating.

* The monarch butterfly is believed to have reached some of the islands it has colonized by hanging into ship riggings.

* The monarch makes its migratory flight at speeds of up to 11 miles per hour. It travels up to 17 feet above the ground.

Biology

Unlike most other insects in temperate climates, Monarch butterflies cannot survive a long cold winter. Instead, they spend the winter in roosting spots. Monarchs east of the Rocky Mountains fly south to the forests high in the mountains of Mexico in the state of Michoacan (150miles west of Mexico City near El Rosario). There the Mexican Government has set-up a Monarch sanctuary.  Monarchs sometimes cover it's preferred host, the Oyamel Fir, top to bottom. The migration is driven by seasonal changes. Day length and temperature changes influence the movement of the Monarch.

Monarchs are the only butterflies to make such a long, two-way migration every year. Amazingly, they fly in masses to the same winter roosts, often to the exact same trees. It will take about five generations to make the complete round-trip.

Some other species of Lepidoptera (butterflies and moths) travel long distances, but they generally go in one direction only, often following food. This one-way movement is properly called emigration. In tropical lands, butterflies do migrate back and forth as the seasons change. At the beginning of the dry season, the food plants shrivel and the butterflies leave to find a moister climate. When the rains arrive, the food plants grow back and the butterflies return.

Migration
In late summer and early fall, Monarchs emerging from their pupae, or chrysalides, are biologically and behaviorally different from those emerging in the summer. The shorter days and cooler air of late summer trigger changes. Even though these butterflies look like summer adults, they won't mate or lay eggs until the following spring. Unlike other generations, these monarchs have a little fatty area where the sugar of the nectar is converted into fat. They live off these fatty deposits and only need water to rehydrate their bodies. This fall generation can also live up-to eight or nine months versus only one month for the other generations.

Otherwise solitary animals, they often cluster at night while moving ever southward. If they linger too long, they won't be able to make the journey; because they are cold-blooded, they are unable to fly in cold weather. (The picture on the right was taken by Liesel on 9/4/92 during an extra heavy migration).

Fat, stored in the abdomen, is a critical element of their survival for the winter. This fat not only fuels their flight of one to three thousand miles, but must last until the next spring when they begin the flight back north. As they migrate southwards, Monarchs stop to feed on nectar, and they can actually gain weight during the trip! Some researchers think that Monarchs conserve their "fuel" in flight by gliding on air currents as they travel south. As you watch them pass by you may observe this yourself and you wonder if they make it at all if the cooler north-west winds prevail.

A mystery is how Monarchs find the over-wintering sites each year. Somehow they know their way, even though the butterflies returning to Mexico each fall are the great-great-grandchildren of the butterflies that left the previous spring. No one knows exactly how their homing system works.

Interesting Links

This link contains hundreds of myths and superstitions humans have conjured up over centuries. Quite some interesting stuff!

Everything related to Butterflys (butterflywebsite.com).