The Illinois Tollway board Thursday agreed to explore adding milkweed to roadsides along I-90, I-88 and I-294 to beef up the dwindling population of the state insect – the Monarch butterfly.

In roadsides targeted for Monarch habitat, Tollway grass would be mowed only once a year, instead of the typical two times. Also, the grass would be cut higher than normal and herbicides would be restricted.

Milkweed, which Monarch caterpillars feed on, would be added to the roadside seed mix.

Tollway board members advanced the plan after learning that the Monarchs’ population has dropped precipitously with the increase in the use of pesticides, especially Roundup, in the last 10 years. Such pesticides kill off milkweed, which is the only plant on which Monarch butterflies will lay their eggs.

Illinois is a summer breeding ground for Monarchs during their annual trip from as far north as Canada to central Mexico. Some 550 million completed the trip in 2004, but by 2013, only 33 million arrived in Mexico, according to National Geographic.

The caterpillars that become Monarch butterflies depend on the milkweed plant to survive.  |  Sun-Times Library

The caterpillars that become Monarch butterflies depend on the milkweed plant to survive. | Sun-Times Library

The butterflies are more than just pretty, Tollway officials noted. They are an important pollinator of crops.

Tollway chairwoman Paula Wolff cautioned that some communities “may not be interested in having milkweed” — whose seed pods spout feather-like insides — growing along the roadway.

“We have to be sensitive to the culture of communities,” Wolff said. “We don’t want people getting alarmed.”

Bryan Wagner, Tollway environmental policy and program manager, assured Wolff that the Tollway “won’t just wholesale plant [milkweed] throughout the system. We want to make sure they are targeted and in an appropriate area.” Exact sites have not yet been identified.

In addition, the Tollway hopes to add milkweed to some of the 483 acres of wetland mitigation sites it currently helps maintain – at Lake County’s Pine Dunes, Will County’s Orland Grassland South, and DuPage County’s Springbrook Creek.

Rebecca Riley of the National Resource Defense Council told Tollway board members that when she was growing up in Monmouth, Ill., teachers traditionally would gather caterpillars from milkweed plants so students could watch their development into Monarch butterflies.

But these days, Riley said, “I hear teachers are struggling to find caterpillars.”

The Tollway will be working with the Natural Resources Defense Council in its Monarch restoration project. Experts noted that a Monarch habitat takes several years to establish and, if anything, the plan could save the Tollway money by reducing mowing costs.

Other states already are trying to boost the Monarch population, board members were told. The Minnesota Department of Transportation includes four species of milkweed in its roadside plantings, and the Wisconsin Department of Transportation began planting milkweed this past growing season.