Milkweed flower and buds. We have Milkweed among our flowers because they are used by Monarch butterflies as a place to lay their eggs. When the caterpillars begin eating the leaves of the Milkweed they emit a signal (a sound I have been told) that attracts Wasp which kill and eat the caterpillars. And, when the Wasp appear to attack the caterpillars they look for Monarch eggs and lay their own eggs close to those so that when their eggs hatch they can eat the Monarch eggs. That cycle is the reason that when we see the caterpillars starting to come under attach we bring them into little cartons we keep in the house until they turn into butterflies. Then we release them. We have seen very few Monarchs since the spring.