New plant invader a threat to both monarch butterflies and Fort Wayne’s flood-control levees

Black swallow-wort, an invasive plant that somewhat resembles milkweed, has been found in Fort Wayne and city officials are working to prevent it from spreading. (Courtesy of Early Detection & Distribution Mapping System)

Black swallow-wort is a plant invader that is double trouble, and it’s now been found for the first time in Fort Wayne.

The plant resembles a vining milkweed, but it contains toxins that can kill monarch butterfly caterpillars feed on it, said Ben Hess, landscape manager for the city of Fort Wayne’s Public Works division.

Likewise, the toxins in black swallow-wort also inhibit the growth of other plants around it, meaning it can kill off grass on earthen flood-control levees and expose the soil to erosion during flooding, said Patrick Zaharako, city engineer.

Originally from Europe, black swallow-wort appears to have been brought to America in the 1800s by people moving to this country, Hess said.

The plant, also known as black dog-strangling vine, since has taken hold mostly in Great Lakes states and in northern New England. For more details about the plant and a map of where it has been reported, click here for information from the Invasive Plant Atlas of the United States.

Black swallow-wort spreads by releasing seeds from pods similar to milkweed, so the seeds can spread easily by floating in both the air and in water, said Freya Berntson, volunteer and preserves and programs coordinator for Little River Wetlands Project in Fort Wayne. The organization’s nature preserves include Eagle Marsh off Engle Road.

One of Little River’s big concerns is black swallow-wort’s impact on the already-struggling wild population of monarch butterflies. Because the plant is somewhat closely related to milkweed, monarch butterflies may lay eggs on it mistakenly and then the caterpillars can’t eat the plant after hatching, Berntson said. Monarch butterfly caterpillars eat only milkweed leaves.

The city became involved in attempts to control black swallow-wort after it was found in late May in an alley bounded by Columbia Avenue on the north, Dearborn Street on the east, Edgewater Avenue on the south and Loree Street on the west.

It reportedly also was found in a few places on the flood-control levee along the Maumee River along Edgewater Avenue in the Lakeside neighborhood, as well as at the base of that levee near the street, Zaharako said.

City officials don’t know how the black swallow-wort arrived in the alley or on the levee.

City crews have been spraying the plants on the levee with herbicide to prevent them from spreading, but black swallow-wort is difficult to kill, Hess said.

“From what we have seen so far, it looks manageable,” he said of keeping the invader in check.


* City of Fort Wayne Public Works division officials recommend using the Great Lakes Early Detection Network smartphone application to report the sighting and location of possible invasive plant species.

To make a report, a person uses his or her smartphone to take a photo of the suspected invasive plant, and then sends it to the Great Lakes Early Detection Network, said Ben Hess, landscape manager for the city of Fort Wayne’s Public Works division.

The Nature Conservancy then will send out a field representative to check out the plant.

* You also can report sightings of possible invasive plants at the Early Detection & Distribution Mapping System website.


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