Spongy Moths in Illinois

The caterpillars escaped the lab and began invading the hardwood forests of North America. As it can feed and survive on over 300 species of plants, it began spreading quickly.

Spongy Moths can spread in 2 ways: 1 is naturally, newly hatched caterpillars hang from tree branches on silken threads, allowing themselves to be picked up in the wind. This is called ballooning. As the caterpillar grows larger they can only crawl.

The 2nd way of spreading occurs when people inadvertently transport one of the life stages from an infested area on a car or recreational vehicle, lawn furniture, firewood, logs, nursery stock and other outdoor items

Spongy Moth life cycle:

Eggs are laid in a hairy-like, brownish tan mass in late July thru early September.

Larva: Spongy moth caterpillars will begin emerging from the egg masses and begin to move up into the tree canopy and start feeding on the leaves.

Pupa: caterpillars will stop feeding, and pupate. While in the pupa cases they transform into moths. This process usually takes about 2 weeks.

In late June thru early July the moths emerge from the pupa cases.  Their only mission is to mate and lay eggs. They do not feed during this stage. Since the female does not fly, she has to put out a pheromone scent to attract the males to her. Once they mate and lay their egg, the moths die. This stage lasts approximately 2 weeks.

Starting in May, The Illinois Dept of Agriculture Staff & USDA Staff place traps throughout Illinois for detection. Since female SM does not fly, the pheromone (sexual attractant) in these traps only attracts male Spongy Moths, nothing else. The traps are then taken down in September and the dead moths are counted.

In the 'Slow the Spread' area of Illinois, trap counts are counted and compared to counts in other states in the program. The US Forest Service decides on areas that need to be sprayed for the next year.

In areas of high 'hot spot' populations in the "Slow the Spread" areas, the Illinois Dept of Agriculture manages applications of Bacillus thuringiensis kurstaki (Btk). Btk applications target early instar (baby) caterpillars soon after egg hatch in the spring. Caterpillars must feed on the bacteria crystals to be killed. This is very specifically timed and targeted in these areas and usually in May. The IDA watches weather and size of the caterpillars for timing. A second application is sprayed 7-10 days after the first spray.

Mating Disruption spraying for control of lower populations in the "Slow the Spread" area: Since the females do not fly, the males fly around the area looking for females, but are confused by the pheromone in the spray, so they never find a female to mate. This product is sprayed by yellow airplanes in late June before the moth emerges.

Approximately 65,000 pheromone-baited insect traps are placed annually within the STS action and monitoring areas, with the assistance of state collaborators, who also use STS methods and resources to trap areas in front of the STS action zone. States participating in STS hire about 200 seasonal trappers every year to place and monitor traps. Traps are used to detect low-density populations, predict Spongy Moth spread rate, and evaluate the efficacy of treatments. 

State collaborators manage applications of Bacillus thuringiensis kurstaki (Btk), whereas the USDA Forest Service manages mating disruption applications in the STS program. Btk applications target early instar caterpillars soon after egg hatch in the spring. Caterpillars must feed on the bacteria crystals to be killed. 

Mating disruption applications occur mid-summer and prevent male moths from successfully mating with females. Mating disruption only impacts male Lymantria dispar. 

This map shows the Federal Quarantine for Spongy moth and these areas are considered generally infested

Spongy moths occasionally fill the forest & neighborhoods with hungry caterpillars. Although they can eat all the leaves on trees and are unpleasant to be around, they rarely kill the trees they defoliate. Most healthy deciduous trees (oak, birch, etc.) can withstand a year of complete defoliation and will produce new leaves later in the summer or the following year. However, if spongy moths attack coniferous trees (pine, spruce, etc.), sickly trees, or defoliate deciduous trees two years in a row they may kill them.

Today, spongy moth outbreaks are cyclical, peaking approximately every seven to 10 years. In these years, the virus, Nucleopolyhedrosis, and the fungal disease, Entomophaga maimaiga, a fungal pathogen found to be killing spongy moth caterpillars are spread more easily through dense populations, eventually causing a crash

Based on what we have observed this year, the pathogens that often keep spongy moth populations in check are present, but have not infected enough caterpillars to guarantee a low caterpillar population next year. Therefore, the most important action you can take to protect your trees is to be vigilant this fall and next spring. This fall, make note of how many egg masses you see on your trees and remove any you find. Next spring, look for spongy moth caterpillars around the time that redbud trees start to flower. Spongy moths often go unnoticed until they are already big enough to defoliate trees so it is important to keep careful watch on your trees and respond at the first signs of damage. If we have a dry spring it is more likely that we will have another outbreak because the fungi that attack spongy moth only thrive in humid weather.

If your neighborhood had an outbreak of spongy moths this year, take precautionary measures to prevent another infestation next year. Spongy moths can move between trees so community wide management plans are the most effective. In addition, many treatments are less expensive if a group of trees are treated at the same time. Remember, spongy moths seem overwhelming but can be managed with attentiveness and forethought.

Just after spongy moth eggs have hatched and caterpillars are small, barrier bands can prevent them from climbing back into trees after ballooning or when they have fallen. Barrier bands can be made using duct tape or other nonporous material that can be wrapped around a tree trunk and coated with a commercially available sticky material such as TangleFoot® or Vaseline®. NEVER put sticky material directly on the tree trunk.

If you choose to use pesticides to control spongy moth caterpillars, they must be applied at this time to target the caterpillar stages. There are two options: biological and chemical pesticides.

Bacillus thuringiensis Kurstaki (BtK) used against spongy moth only affects caterpillars of moths and butterflies that feed on treated leaves. Btk has no affect on other animals, birds, people, or even other insects. It is sold under various labels (e.g., Dipel, Foray, and Thuricide). Btk must be applied to trees in May when caterpillars are less than 1/2-inch long. Timing is critical as Btk is significantly less effective on older/larger caterpillars. Some Btk products are available to the public at hardware stores and garden centers.

Chemical insecticides. Numerous conventional insecticides are labelled for control of spongy moth caterpillars in Illinois. Some of these products are intended for use by tree care professionals, while other products may be available at your local garden center or hardware store. Check the label to make sure spongy moths (formerly known as “gypsy moths”) are listed on the label.

If you are moving to a new hom​e from a spongy moth quarantined area to a non-quarantined area, you could unknowingly introduce spongy moth to a new location. Anything that you keep outdoors could hide spongy moth egg masses: patio furniture, bikes and other play things, building materials, camping equipment, birdhouses, gardening equipment, plant containers, and even vehicles. If you do find egg masses, you can scrape them into soapy water for one to two days to destroy them.

Don’t transport to campgrounds or parks. Buy locally harvested or certified firewood. Ask a park ranger or campground host about where to get local firewood.

A new study estimates that over the next 30 years, 1.4 million street trees will be killed by invasive insects, costing over 900 million dollars to replace.

The photo to the right, is spongy moth damage just north of us in Wisconsin.