Columns, The Outside Story

Spring is Fleeting for Butterfly, Wildflower Host

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WHITE RIVER JUNCTION – It’s not a gaudy butterfly. It isn’t the biggest or the smallest. In fact, it’s mostly just white. But this butterfly is unusual: It only flies in forests. To see this butterfly, you must visit a rich, mature hardwood forest carpeted with spring wildflowers. West Virginia Whites fly slowly and close to the forest floor. Follow a woodland stream until you find the host plant and the butterfly.

photo by Kent McFarland
Spring form Mustard White butterfly.

The West Virginia White is almost completely white above, with some gray scaling on the forewing. Below, the wings are whitish, with veins outlined in pale gray scales. It is often confused with the Mustard White, which, by contrast, shows distinct, dark green-black veins on the underside of the hindwing during its spring flight.

Adult butterflies sip nectar from spring ephemeral wildflowers like toothwort (Cardamine), Spring Beauty (Claytonia virginica), violets (Viola), and others, perhaps pollinating some of them along the way. Their caterpillars only feed on toothwort and rock cress (Boechera). Like the flowers they feed on, West Virginia Whites are also spring ephemerals.

photo by Kent McFarland
Two-leaved Toothwort (Cardamine diphylla)

Spring ephemeral wildflowers are perennial woodland plants that sprout from the ground early, bloom fast, and then go to seed, all before the canopy trees overhead leaf out. This allows plants to take advantage of full sunlight reaching the forest floor during a short time in early spring. Once the forest floor is deep in shade, the plant’s leaves wither away.

Closely tied to healthy hardwood forests, some West Virginia White populations are declining or have disappeared through loss of forest habitat, high populations of deer overbrowsing understory plants, climate change, and the spread of an introduced weed called Garlic Mustard (Alliaria petiolata).

Garlic Mustard was first found in the United States around 1868 on Long Island, N.Y., and spread throughout the butterfly’s range. Adult butterflies are fooled by Garlic Mustard. The chemistry of the plant makes it inviting for females to lay eggs on the leaves, but once they hatch, the caterpillars quickly die from ingesting alliarinoside, a compound unique to Garlic Mustard. When it is present, the butterflies place nearly two-thirds of their eggs on Garlic Mustard rather than a native host plant.

photo by Kent McFarland
Closeup of Garlic Mustard flower and leaves

You have to hurry to see this butterfly. As soon as the canopy leaves burst and shade the forest floor, the adults are gone until the next year.

Help us track butterfly populations and contribute to the second Butterfly Atlas by adding your surveys and sightings on eButterfly (e-butterfly.org/ebapp/en/projects/view/22), that records the presence or absence of species and abundance through checklist data. A checklist is one or more observers like you going out for a known amount of time over a known distance and recording all species and individuals encountered. This is the most valuable information for understanding butterfly ranges, abundance, and seasonality. Grab your camera and start recording butterflies for fun, science, and conservation.

Kent McFarland is on the staff of the Vermont Center for Ecostudies.

Kent McFarland

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