Spongy Moth

The Forestry Division is very active in preventing and mitigating tree pests. The Forester coordinates with the Morton Arboretum and the Illinois Department of Agriculture to survey parkway trees. During the year, with the help of residents, public infested trees are monitored for insect activity and addressed accordingly.


Lymantria Dispar, or spongy moth, are an invasive species known for tree defoliation. Preferring oak species, a single moth can consume 11 square feet of vegetation during its lifetime. During large outbreaks, trees are virtually stripped of their leaves by hungry caterpillars within a few days. Although most trees will re-grow new leaves before summer's end, the process stresses the tree and drains its reserves. Weakened trees and shrubs, especially those in urban settings, are more susceptible to attack by opportunistic diseases and organisms. In addition, the tree's growth rate is impaired, which affects its chances for survival during the following years.Spongy moth

Eradication Treatments

The Illinois Department of Agriculture and USDA APHIS, along with the STS Foundation, place over 10,000 traps to monitor populations each year. Each year, the monitoring is tabulated, and eradication treatments, usually aerial applications, of Btk (Bacillus thuringiensis kurstaki) or mating disruption are decided for the following year.

Aerial applications of BtK are applied from aircraft to areas where spongy moth threaten trees and the public. If chosen to be applied, a series of two treatments are occur in early May, when caterpillars are small and most susceptible to BtK. When eaten, the protein crystals in BtK tear the cells that line the intestine of susceptible insects, causing them to die from bacterial infection.

Is BtK Insecticide Safe?

Yes. BtK bacteria do not cause diseases in people, mammals, birds, or fish. BtK insecticide can cause some minor and temporary irritation to exposed skin, eyes, ears, nose, and throat. However, numerous studies of large communities of people exposed to Btk during aerial sprays for spongy moth and other caterpillars have repeatedly failed to find any significant adverse risks to the health of the general public.

Will BtK kill other non-native species?

Yes, but they will not eliminate them. BtK only kills butterflies and moths that are in the caterpillar stage. Most of Illinois’ butterflies, including Monarch butterflies, are not in the caterpillar stage until over a month after the aerial spray, when the BtK protein has degraded. The spray does not contaminate the area with BtK bacteria. Furthermore, only small parts of the forest are targeted for spray. Butterflies outside the spray area are not affected.


Illinois Department of Agriculture Webpage on Spongy Moth

Spongy Moth FAQs

Village Forester PowerPoint on Spongy Moth

Presentation on Spongy Moth at October 19, 2023 Village Board Meeting