Different macroinvertebrates, small creatures or “bugs” without a backbone, have different tolerances to pollution found in water. Pollution in this sense might include, phosphates and nitrates from fertilizer, bacteria, and some heavy metals. Several of these “bugs” are collectively known as Group 1 organisms. All of them happen to be insects, and all have no tolerance to pollution.
Friends of the Chicago River has been monitoring the health of the North Branch of the Chicago River for over fifteen years. In all that time, we’ve never found a Group 1 insect north of downtown. Until recently…
In October 2009, students from St. Ignatius College Prep High School and Maine East High School each found a dobsonfly larvae, also known as a hellgrammite. One was at Glenview Woods, the other at Linne Woods. Both were found in the North Branch of the Chicago River.
Allen LaPointe, Director of Water Systems and Analysis at the John G. Shedd Aquarium, is encouraged by this discovery. “Dobsonflies are an important piece of the puzzle in the Chicago River, along with bigger animals that eat them, like fish and otters. The return of these animals not present 20 years ago says to me that the river is improving.”
Ben Schaufele, a senior and Ecology Club member from Maine East High School, found the dobsonfly on his field trip. Upon learning of the insect’s importance as an indicator of good water quality and of the rarity of his find, Ben stated, “It was a privilege and an honor to find such an interesting indicator species.”
There are almost two dozen species found in North America, but none in the Chicago River until there were found in 2009. Since then, three additional dobsonfly larvae have been found on Friends of the Chicago River field trips. One by Maine East High School again at Linne Woods in October 2010. Two others were found in November 2010 by Christ the King School at Irene Hernandez Family Picnic Area in LaBagh Woods, a site downstream of last year’s discoveries. The larvae appear to be active in the late fall months.
Whether this is a return of the species for good or not is yet to be seen. Only continued monitoring of the river will tell.
Post submitted by Mark Hauser, Friends of the Chicago River