Where Did These Pests Come From?

The first sighting of the zigzag sawfly in the U.S. occurred in Virginia in 2021, and the sawfly has infested 14 other states since then. It's been identified in New York, Massachusetts, Minnesota, and Wisconsin, among others. The newest state on that list is Michigan, which announced its confirmed existence on June 23.

The only Michigan county that is known to have zigzag sawfly pests so far is St. Clair County. But regardless of whether you're in this county, a different area of the state, or anywhere near the path of these sawflies, it's important to know how to identify zigzag sawflies (and what to expect from them if you find any). These invasive sawflies can spread very quickly, but they won't necessarily hit every county in each infected state; five years after they were first identified, many counties are still free of the pest.

How to Tell if Zigzag Sawflies Are Infesting Your Elm Trees

The sawfly gets its name from the zigzag patterns it makes on leaves as it eats. Elm leaves with a zigzag pattern are one sign that you're dealing with a sawfly infestation. If you spot this unique symptom, look for green caterpillar-like larvae on the elm's leaves. You may also see small larvae cocoons on the backs of some leaves. Adult zigzag sawflies look like small, black, winged wasps.

Sawflies aren't picky, and will infest any type of elm, from slippery elms to American elms. If you're in or near a state that has a confirmed sawfly problem, keep a close eye on your local elms trees. Dozens of larvae can infest an elm tree at a time, and they will continually eat through the elm's leaves as they grow. While not all pest infestations will cause significant damage to an elm, if the sawflies manage to destroy most of the tree's leaves, it may struggle with growth in later years.

While the zigzag sawfly is invasive, it isn't a dangerous pest—unless you're an elm tree. They do not bite or sting, and pose no problems for pets, either. However, it's still important to be aware of the damage they could cause to your local elms.

What to Do If You Spot Zigzag Sawflies

Because elm zigzag sawflies are an invasive pest, it's important to report any zigzag sawfly sightings you find. This will help your state track the spread of the infestation and control it as much as possible. Even if zigzag sawflies haven't yet been reported in your county, keep an eye out for them so that your state understands how they spread.

At home, you can hose down an infested elm tree to get rid of invasive sawflies. You can also simply remove the larvae from the leaves by hand. Before doing so, take photos for your invasive pest report.

If you're dealing with a significant zigzag sawfly problem, it's best to call in a professional. Experts say that insecticide or chemical pest control can help with severe sawfly infestations, but you shouldn't attempt these solutions on your own.