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New caterpillar host plants planned for Thuya butterfly garden

This winter we are developing a plan to expand the butterfly garden that is located below the Burden sitting area.

Male and female Atlantic fritillaries (Speyeria atlantis) on phlox

This project will involve reducing and relocating some of the hay-scented fern, Dennstaedtia punctilobula in that area. These ferns were originally planted as a memorial to Henry F. "Nick" Harris (1930-2007), who with his wife Penny were members of the Thuya Garden Committee and longtime supporters. Also, as part of his memorial was a Kousa dogwood, Cornus kousa, planted near the ferns. Unfortunately, the dogwood succumbed to porcupine damage in 2011.

A replacement tree was obtained and planted in the lawn at the other end of the garden, between the well and the pond, where it seems to be thriving. Some ferns were removed when the original butterfly garden was installed in 2013, but the ones that were left have since expanded their footprint, as is their wont. The current plan is to move much (but not all) of the remaining ferns to the area where the new dogwood is currently located.

The expanded butterfly garden will focus on providing caterpillar host plants for many of the butterfly species that we have seen in the garden. There is no lack of nectar plants at Thuya; what many butterfly (and moth!) species need are host plants that will enable successful reproduction, and most species have a narrow selection of plants on which their caterpillars can feed.

Silver-spotted skipper (Epargyreus clarus)

After all, that is why the original butterfly garden included primarily swamp milkweed, Asclepias incarnata, plants not to provide nectar but to allow monarch butterflies to lay eggs and make more monarchs. Other butterfly species can use the same kind of help. (Related factoid: monarchs are not important pollinators for their own host plants: milkweeds are pollinated by a variety of insects, most efficiently by larger bee species such as bumble bees and carpenter bees.)

In developing the planting plan, we researched the host plant needs of the 35 butterfly species we have encountered at Thuya and narrowed the plant list down to those that will be suitable for this area. The plan is to use plants from this list that will grow in this spot without blocking the view from the Burden bench and remain semi-hidden from the borders. The idea is not to attract adult butterflies with nectar plants, but rather to help boost butterfly populations by providing food for them in their caterpillar stage.

Northern crescent butterfly (Phyciodes cocyta) on floss flower

In fact, some of the host plants, such as various grasses, are not significant nectar sources at all. Sad to say, we have seen declines in many of our butterfly species, not just monarchs, in recent years. Although we don't know the cause or extent, we hope this new planting will help mitigate these losses and visitors will have more garden butterflies to enjoy while also learning about the importance of having host plants in their own landscapes.

The expanded butterfly garden will feature caterpillar host plants that will benefit our resident butterflies. For example, the Northern crescent butterfly (Phyciodes cocyta) relies on various native asters such as the hairy white oldfield aster, Symphiotrichum pilosum and the smooth blue aster, S. laeve for food in their caterpillar stage. All the fritillary butterfly species, such as this male and female Atlantis fritillaries (Speyeria atlantis), need native violets, Viola spp., and the silver-spotted skipper (Epargyreus clarus) caterpillars depend on various plants in the family Fabaceae, such as false indigo bush, Amorpha fruticosa and showy ticktrefoil (Desmodium canadense). As can be seen, the nectar food pants for the adults greatly differ from those needed by the young.

We hope to install this new landscape in late June of 2021 with plants grown at our McAlpin Farm production facility, thanks to the support of the Mount Desert Garden Club. As with any new landscape, it will look young the first year and will mature in its second and third year. Be sure to come watch it evolve.

Rick LeDuc, Thuya Garden Manager

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