not sure what it is called a plant or a bush..
Do a Google search for the genus Buddleja, these are the butterfly bushes. Asclepias (milkweeds) are another genus important to butterflies as a nectar source and as a host plant for Monarch butterflies during their larval stage.
Here is a good site for information on Asclepias species as well as seeds of the various species. Growing our common Asclepias syrica is becoming more and more important as this plant is becoming quite rare in many rural areas due to herbicide use. Last summer while visiting family in south Bruce county area of Ontario I spotted only a single unhealthy plant. Farmers do not want this plant to contaminate their hay crops but the monarch butterflies are the ones who loose out in the end. There are large areas of Asclepias syrica in the London area but I am not sure how common this plant is where you are? Growing a few of these drought tolerant plants in your garden will more than likley attract the butteflies and allow you to watch their next generation develop. Many people view these plants as weeds but they are easily one of my favorite native plants.
Here is a link that might be useful: Milkweed Farm