The spongy moth is back.

It may be cute, but it’s also hungry, not picky – and dangerous for trees.

Riverside trustees have agreed: No more.

The invasive species will be treated in affected areas with aerial applications of Btk, a naturally occurring insecticide. Those applications will likely occur in May 2024.

The preliminary decision came after a presentation given by village forester Michael Collins.

“It’s definitely alarming,” Collins said. “Finding the infestation alone is definitely a huge red flag in terms of our tree population.”

Residents reported spongy moth sightings in the Scottswood Common area to the public works department in July. 

The insects are a nonnative, invasive species, first introduced to North America during the 19th Century. They have no natural controls or predators that balance the population of the moths and their impact on a landscape, so “control is an important consideration,” Collins said.

At an October village meeting, Scott Schirmer, the Nursery and Northern Field Office Section Manager of the Illinois Department of Agriculture explained that spongy moths defoliate trees during a caterpillar stage that occurs in the spring. And according to the U.S. Department of Agriculture, they have a taste for more than 300 types of trees and shrubs. They defoliate their targets, which leaves them vulnerable disease and pests. Repeated defoliation can kill the trees. 

“Spongy moth can be fairly impactful to our tree population and especially the area where it’s been discovered has a high population of oak trees, which are their preferred host,” Collins said.

Schirmer also explained the other consequences caused by an infestation, such as increased noise levels, decreased shade, reduced property values and homeowner liability for fallen tree limbs and tree removals.

“Any time you have something attacking trees or causing damage on trees, it hits people at home, especially in Riverside,” Schirmer said at the meeting.

Collins presented three management options for mitigating the presence and spread of spongy moth. One course of action was a monitor and evaluate approach that included moth trapping, while a second possibility was ground applications of insecticide. Collins said that applying the treatment by ground, however, is less effective and more expensive than by air. 

The final option, which trustees agreed to implement, was two aerial applications of Btk, a naturally occurring soil-borne bacteria that only kills caterpillars. It does not affect humans or other animals.  

Schirmer said Btk minimally impacts caterpillar species native to the area. Some species have not yet hatched into the caterpillar stage when Btk is applied in spring and thus cannot be affected. The habitats of spongy moth and monarchs, meanwhile, “don’t cross over significantly,” Schirmer said.

“Even if you do have some collateral damage, you remove the spongy moth as a primary competitor for the natives,” Schirmer said at the meeting. “The natives have more background noise in the area, so they spill back in a lot quicker and rehabitate that area with less competition.” 

This is not Riverside’s first bout with spongy moth. Collins said he found egg masses in 2005 within Scottswood Common and Indian Gardens.

 In 2006, parts of Riverside, Brookfield and Lyons, received aerial applications, while ground treatments were conducted in certain spots in 2009, according to Collins.

Riverside residents can learn more about spongy moth and treatment against the insect at the village’s website.