Determine whether the estimates of Monarch Watch are more or less on track. Why Butterflies Are in Danger Monarch butterflies are in danger of losing both their summer and winter habitats. As land is developed, milkweed is killed. This is the only source of food for monarch butterfly larvae once they hatch from their eggs. Milkweed plants are also vulnerable to herbicides used by farmers, homeowners, landscapers, and gardeners.
Herbicides are poison substances used to inhibit weed growth in gardens, lawns, and fields.
The butterflies don't have it easy in Mexico, either. The ovamel trees that they winter in also serve as a lumber source for local communities and big logging companies. Logging not only removes the trees, it opens up the forest canopy. The overhead holes expose the butterflies to the elements, increasing the chance that they will die. There are only about a dozen known wintering sites in Mexico.