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Corps of Engineers discovers fall webworms on Mississippi River island

Published Sept. 16, 2014

ST. PAUL, Minn. – The U.S. Army Corps of Engineers, St. Paul District, recently discovered fall webworms have returned to an island along the Mississippi River near La Crosse, Wis. 

The U.S. Fish and Wildlife and Corps recently conducted a site visit on Red Oak Island, in Pool 7, and determined 90 percent of the trees were infected with webworms. The outbreaks occur about every four to seven years and generally last around two to three years. The fall webworms eat most of the late-season foliage, but are unlikely to kill trees nor do they pose any threats to people.

A native pest to North America, the fall webworm feeds on more than 85 species of trees within the United States, including walnut, American elm and bitternut hickory. They grow to about an inch in length and are brown and tan with long, white hairs. The adults emerge from late May into July. 

The fall webworm was first noticed on the island in 2003. Foresters will continue monitoring the forest health on the island and will revisit the area next spring to determine whether the webworm population is declining as expected.  

The nearly 650 U.S. Army Corps of Engineers, St. Paul District, employees working at more than 40 sites in five upper-Midwest states serve the American public in the areas of environmental enhancement, navigation, flood damage reduction, water and wetlands regulation, recreation sites and disaster response. Through the Corps’ Fiscal Year 2011 $175 million budget, nearly 2,800 non-Corps jobs were added to the regional economy as well as $271 million to the national economy. For more information, see


Public Affairs

Release no. 14-083