In Mexico they roost on oyamel pine trees. Logging has already drastically reduced their habitat, so that only a few islands of proper oyamel forest remain. Even so, the deforestation around the preserves weakens the ability of the forest to moderate temperatures, and now the butterflies die of frost that formerly could not penetrate to their habitat. Because monarch butterflies live in Mexico and in the northern United States and Canada, one country alone can't preserve them. They need enough habitat and food in both their ranges.
Monarch caterpillars eat nothing but milkweed leaves.
Pulling up milkweed in the United States threatens them just as much as deforestation in Mexico does. You can find out more about monarch butterflies from Monarch Watch . In the southeastern mountains, in Catemaco, some corn farmers use velvetbean as a companion plant. The velvetbean, planted thirty to fifty days after the corn, grows rapidly, squeezing out weeds by depriving them of sunlight. The corn, already established, grows tall enough to reach the sunlight.