Are creeping caterpillars spoiling your early summer fun or harming your trees? Gypsy Moth caterpillars are making messes and gobbling tree leaves in larger than normal numbers this year in many yards, parks and natural areas around the Thumb Coast.
This exotic invasive forest pest was introduced into the U.S. over 150 years ago and has been posing ecological threats ever since. The caterpillars hatch in late spring from egg masses laid the previous fall. The tiny, hairy, hungry caterpillars begin dispersing and feeding as the tree leaves unfurl, and they spend the next few weeks growing into two to three inch long leaf eaters. Their favorite food is oak leaves, although they will feed on many tree and shrub species.
Leaf removal, also known as defoliation, comes at a bad time for the trees–when they’ve recently spent their energy to flower and leaf out. Most trees and shrubs will have enough health and vigor to put out a fresh set of replacement leaves so that they can photosynthesize and feed themselves once again. Developing this second set of leaves, however, can use reserves that might have been better spent getting through a hot summer, fighting off other pests and stress, expanding root systems, or storing away energy for the winter. Trees and shrubs that are significantly defoliated can be set back or even killed if this happens early in the season for more than a couple of years in a row. It’s also a very stressful time for people. The leaf fragments and frass (caterpillar dung) raining down from the trees, loss of shade, and sheer numbers of large hairy caterpillars are enough to drive homeowners and trail users to flee or take cover indoors.
What can you do?
First, don’t panic. Like any other pest, Gypsy Moth populations are cyclical. While they may be numerous, annoying and destructive at times for the next year or three, eventually they will dwindle as overpopulation intensifies and natural enemies regain control. The only stage of the life cycle that’s harmful to trees is the caterpillar phase, so most of the damage and aggravation will stop in July as the caterpillars move into their pupal phase before metamorphosing into adult moths and laying egg masses.
Second, take action. Keep your trees and shrubs as healthy as possible and do what you can to reduce caterpillar numbers around your home and outdoor spaces. Water valuable shade trees during hot, dry weather and avoid damaging roots. Consider using hiding bands to protect individual trees or your favorite gathering places. Hiding bands are flaps of burlap fastened around the trunks of trees at a comfortable working height. Flick the caterpillars you find in the bands into a can of soapy water each day in the late afternoon to reduce the number of larvae and the amount of frass raining down on your patio. Never handle caterpillars with your bare hands as their urticating hairs may give you a stinging, burning rash.
Third, communicate. If you have caterpillar issues it’s likely your neighbors and community members do, too. Share your concerns and learn from each other what works best to manage infestations and quality of life. Let your township or city and county officials know you’re experiencing these challenges so that they can help determine the extent of the problem and develop ideas for mitigating it. Take photos of the caterpillars and damage and submit your findings to the Midwest Invasive Species Information Network (MISIN) smartphone or computer app at https://www.misin.msu.edu/. This database is used by agencies, researchers, land care professionals and citizen scientists to monitor invasive species outbreaks and provide support for management.
By late summer, Gypsy Moth populations will have laid egg masses that will overwinter to start the cycle all over next spring. Watch for an upcoming article about egg mass surveys and steps you can take through the fall and winter. Friends of the St. Clair River and the Lake St. Clair Cooperative Invasive Species Management Area are partnering to deliver public education and raise awareness of local invasive species issues such as Gypsy Moth. Reach out to us at firstname.lastname@example.org with questions and for more information.
Do you have nature stories or observations you’d like to share? Leave us a comment!