Ask EcoBeneficial!

A friend just told me that Butterfly Bush is not as helpful to butterflies as we might have thought from the name.  Why is this and what should I plant in New Jersey?

Answer

There has been a lot of press recently about the serious decline of Monarch butterflies.  This has sparked greater interest in how to support butterflies.   While we typically associate butterflies with flowering plants that provide them with nectar, this is only part of the story.

Adult butterflies have a completely different diet when they are wee caterpillars.  Most caterpillars are strict herbivores and only eat plant leaves.  The catch is – they cannot eat just any plant leaves, they must eat the leaves of plants that their particular species has evolved with. These plants are known as “host plants.”   Adult female butterflies seek out host plants on which to lay their eggs, so that their emerging caterpillars have a food source.

Different species of butterfly caterpillars have different host plants.  Some caterpillars have a wider array of host plants than other caterpillars.  For example, the Eastern Swallowtail caterpillar can eat the leaves of Magnolias, Tulip trees, Cherry trees, Ash trees, Basswood, Willows, etc.   In the case of Monarch caterpillars, however, they can only eat the leaves of Milkweed species (Asclepias species).  No Milkweeds = no Monarchs.

Some plants, including Milkweeds, can be host plants to caterpillars (Monarchs in this case) as well as nectar plants to a wider array of adult butterfly species.  While Butterfly Bush (Buddleia davidii) is an attractive nectar source for butterflies, it is an exotic, non-native plant from Asia which has not evolved with our butterfly species.  Accordingly, Butterfly Bush does not serve as a host plant to any of our native butterfly caterpillars.   In addition, in some parts of the country, Butterfly Bush has been found to re-seed aggressively, out-competing native plants, earning it a place on the “invasive plant list” in several states.

What should you plant?  The best practice is to plant both host plants and nectar plants, emphasizing regionally native plants that have evolved with the butterflies in your area.  There are many wonderful resources that can help you.  Take a look at the plant lists provided on the Xerces Society website:  www.xerces.org, check out any lists provided by your local native plant society, and pick up the valuable book:  Caterpillars of Eastern North America, by David L. Wagner, one of the best sources of information on host plants in the East.

Last but not least, make sure that you include some Milkweeds in your landscape for our tremendously threatened Monarch butterflies.  There are a number of Milkweeds native to New Jersey including:  Asclepias incarnata (Swamp Milkweed – but it does not need a swamp!),  Asclepias purpurascens (Purple Milkweed), Asclepias tuberosa (Butterflyweed),  Asclepias syriaca (Common Milkweed – can be aggressive, so best used in more natural areas),   Asclepias verticillata (Whorled Milkweed),  and Asclepias exaltata (Poke Milkweed).

Thanks for the great question!

Kim