A Butterfly’s Guide to Plants

by Barbara Walvoord

So you’re a butterfly. You need nectar to eat. Plants do their best to produce nectar that you and lots of other insects can eat, because they want you to come for the nectar, get your body full of pollen (which carries the male seed), and carry the pollen to female parts of the same or other plants. Alien plants that have come here from Asia, Europe, or Africa also make nectar, and if the plant structure allows you to get your mouth in there, you can get their nectar. Great! A butterfly garden with alien plants works quite well for nectar. Butterfly bush? It’s an alien, classified as invasive, but who cares? It has nectar. Bring it on. Purple loosestrife? Sure, it’s taking over wetlands and driving out turtles and ducks, but who cares? It has nectar. Bring it on!

BUT WAIT. As a butterfly, you came from a larva–a caterpillar. The larva hatched from an egg laid on a plant by a female butterfly. As a responsible mama butterfly, you want to lay your eggs only on plants that your larvae can eat. As a larva, you don’t eat nectar–you eat leaves or stems. And not just any leaf–only the leaves of one, or perhaps just a few, plants.

Plants don’t like to be eaten, so they develop chemistry hostile to larvae. But YOUR larvae have developed ways to overcome the defenses of one, or a few, species of plants. If you’re a black swallowtail larva, only plants in the carrot family. If you’re a monarch larva, only milkweed.

That’s why a gardener who wants to support butterflies can choose nectar-producing plants, but also “host” plants that larvae can eat.

In our meadows at Lathrop now, you’ll see blooming some common natives on which butterflies and moths (Lepidoptera) are very busy laying their eggs. Native aster supports 105 species of Lepidoptera, sunflower 73, and Joe Pye weed 40. At our meadow edges, native cranberry supports 286 species of Lepidoptera, serviceberry 119, and dogwood 115. In our forests, oak supports 518 species, and maple supports 287 (http://udel.edu/~dtallamy/host/). Controlling invasive plants helps keeps our land a rich nursery for butterflies. At Lathrop, we strive not only to PLANT butterfly gardens, but to BE a butterfly garden.

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