Mr. Morales: Every fall, millions of monarch butterflies fly from the northern United States and Canada to a small area of mountain forests in central Mexico. Because of where it sits on the map, Texas is on the main route for many of them, both on the way south in October and on the way back north in the spring.

Mr. Morales: What surprises most people is that no single butterfly makes the whole round trip. The monarchs that fly south in the fall are a special generation. They can live up to eight months, while summer monarchs live only a few weeks. They spend the winter crowded together on trees in Mexico, and in early spring they start north and lay their eggs in Texas.

Mr. Morales: Those eggs become butterflies that live only a few weeks, so it takes several short generations to reach the northern states again. The monarchs that arrive in Canada in summer may be the great-grandchildren of the ones that left.

Mr. Morales: Here's the important part. Monarch caterpillars can eat only one kind of plant: milkweed. If the butterflies coming north can't find milkweed in Texas to lay their eggs on, the whole journey north is in trouble. That's why planting native milkweed, even in a school garden, really helps.