Milkweed is toxic to some livestock, so should not be grown in gardens, argues W. Langenberg. Many plants are toxic to a variety of animal species – after all, chemical warfare is one of the few defensive options available to plants. And we should be grateful for this since many medicines are derived from the toxic chemicals that plants produce.
Milkweed species are native to Ontario and other parts of North America, and by definition cannot be invasive in their native range. Since the arrival of Europeans, native plants have been greatly reduced in number to make way for housing, agriculture, horticulture and other human land use development. Native plants have also been replaced with non-native plants, some of which are invasive. Doug Tallamy, a Professor of Entomology, has been one of the driving forces behind the increased interest in native gardening. His work shows how vital native plants are for supporting native insects, with particular focus on butterflies and moths. Butterflies are beautiful in their own right, and are vital pollinators, and caterpillars are key food sources for birds. Reduced native plants means reduced insect populations which leads to reduced bird populations.
Many butterflies and moths are highly specialized in the plants they can eat, with some species reliant on a single host plant species during their caterpillar stage. Milkweed species are the sole host plants for the endangered Monarch butterfly in its caterpillar form, as well as supporting a number of other invertebrates.
We are seeing significant declines in invertebrates due to climate change, habitat loss, and insecticides. We should be planting native species wherever possible and removing non-native species, particularly invasive species such as periwinkle, goutweed, bindweed, and Norway Maple.