Monarch Watch 2000 in Central Park

 Dana Discovery Center * Belvedere Castle * Wildflower Meadow

 Butterfly Metamorphosis     July 19, 2000 to September 16, 2000

Monarch Tagging Event      September 22, 2000

Migration

 In all the world, no other butterflies migrate like the Monarchs of North America.

Because Monarchs are unable to survive through a long, cold winter they travel to roosting spots in warmer climes. Monarchs west of the Rocky Mountains settle in groves of trees along the California coast. Those east of the Rocky Mountains fly farther south, to forests high in the mountains of Mexico. A Monarch may fly as many as 3,000 miles to get to its winter roost.

The monarch knows when to migrate by seasonal changes. As summer ends the days get shorter and temperatures get cooler and somehow the last brood of Monarchs know that it is time to head south.

This final brood of the year is physically and behaviorally different than earlier hatches. It doesn’t mate and lay eggs but instead immediately embarks on its long trip south, during which the butterflies actually gain weight. This extra fat, stored in their abdomens, helps them survive over the winter in their cool roosting spot in the volcanic mountains of central Mexico.

In the spring, as the days warm up, the butterflies mate and then head north, looking for milkweed plants on which to lay their eggs. Timing is of the utmost importance. If they return too early they can get caught up in a freeze and die.

The returning females lay their eggs on milkweeds, the caterpillar’s larval food plant, and then die, eight months after they hatched. Each of three or four new broods mates and flies farther north and thus they repopulate the U.S. and Canada. Until the summer begins to wane and the air gets cooler and the year’s final brood of Monarchs once again turns around and heads south.

Tagging

Because it is impossible to travel with the migrating Monarchs, there are many unanswered questions about the butterfly’s fall trip south. We don’t know how the butterflies know where to go, or how they get there. Do they take the same route each year, or does it vary? We also don’t know if the number of butterflies changes from year to year and whether that’s because of the weather or other changes.

The best way we have to get the data to answer these questions is to tag butterflies as they head south. Each tag has a serial number that lets us know where the butterfly was tagged. When the tags are found later we can compare the place (and date) where they were tagged with the place (and date) where the tag was found. If we collect enough tags we hope to be able to figure out what is going on during migration, even though we can’t be there.

To Tag a Monarch

Catch a butterfly in a net. Use a net at least 24” deep. Cheap shallow nets will often harm the butterfly. It is almost impossible to catch a Monarch in flight. Look for them as they are nectaring on a flower, or while they are in their roosts late in the day or early in the morning.

Approach slowly (from behind if possible) and sweep the net forward quickly, then flip the end of the net bag over the net handle. You want the butterfly in the deep end of the net. With one hand holding the handle, use the other hand to collapse the end of the net. There should be enough space at the deep end to keep the butterfly from being damaged.

Flatten the net bag so the wings of the butterfly are closed over its back (thorax) and place thumb and forefinger over the leading edge of the wings (from outside of net). Next, with your thumb and forefinger, reach in to the net and firmly grasp the thorax. Remove the butterfly for tagging.

The tagging method is simple - remove a tag from the backing, place it over the discal cell and position the balls of your thumb and forefinger over the distal cells on both sides of the butterfly. Press firmly for two seconds and release the butterfly after recording the tag number and other information on the data sheet.