Invasive plant could be factor in Monarch decline

By: 
Linda Gallagher, Contributing Writer

Courtesy photo

An exotic invasive plant that kills Monarch butterfly larvae could be one of the factors in the decline of the species as a whole, according to local experts. Monarch butterflies have seen a severe decline over the last decade in the U.S. Along with the invasive plant, some believe that new types of insecticide and herbicides now on the open market may have caused the decline, while others point to an abnormal winter freeze in the mountains of Mexico where millions of the insects winter each year as a possible factor. 

 

Courtesy photo

Black swallow-wort is an invasive exotic species of plant that when eaten has proven toxic to Monarch butterfly larvae and other insects. The plant has been found near Elk Rapids in Antrim County as well as in surrounding areas of northern lower Michigan. 

 

REGION – Although it is not believed to be firmly entrenched in northern Michigan – yet, an exotic invasive plant that kills Monarch butterfly larvae could be one of the factors in the decline of the species as a whole, area experts said last week.

"It could be a factor," said MSU Extension's Erwin "Duke" Elsner of the black swallow-wort, a plant introduced to the U.S. by nurseries and landscapers in the late 1800s which has proven lethal to the larvae of Monarch butterflies, as well as other insects and some mammals.

The species attracts Monarchs, as well as other types of butterflies and insects, which lay their eggs on the plant. Upon hatching, the larvae die after feeding on the toxic plant.

"There's a lot of factors when it comes to why we have been seeing so few Monarchs in recent years, but this plant – which is common in other states – could be a piece of the puzzle," said Elsner, who holds a PhD in entomology, the study of insects. "It certainly isn't helping."

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