DELAWARE, Ohio (WCMH) – An invasive insect that leaves a pattern on elm tree leaves was detected in Ohio for the first time this summer.

Officials found a population of elm zigzag sawflies at the U.S. Department of Agriculture’s Forest Service Northern Research Station in Delaware in early July. The research station has been growing elm trees for decades, which are the pest’s host of choice.

The insect was also confirmed in northern Franklin County in August. 

Forest Health Program Manager Tom Macy said the invasive bug, native to Asia, has been on the Ohio Division of Natural Resources’ radar since it was first detected in North America.

The invasive insect was identified in Canada in 2020 and the United States in 2021 and 2022. 

“We may find that this insect is more widespread than we realize, and now that people are kind of on the lookout for it we might find it more places,” Macy said. 

The insect larva is up to half an inch long, caterpillar-like and light green in color.  In the fall, they form cocoons on the ground in leaf litter or soil. Adults are about a quarter of an inch long, shiny, black and winged.

“I think they’re going to be the only insect that causes this interesting sort of zigzag pattern that it chews through the leaves,” Macy said. “When the larvae hatches out of the egg they start to feed on the leaves and create that pattern.” 

The extent of the damage these insects cause or how they may affect Ohio is still an active area of research.

“We’re trying to determine just how much damage they might do,” Macy said. “I know last year [in North Carolina], they had almost totally defoliated a large elm tree in someone’s yard. So, they are capable of doing pretty heavy defoliation but they don’t do that everywhere, cause there’s places in Canada and Europe where they’re known to occur that they don’t seem to cause much of a problem.” 

Macy said it is likely they will spread quickly, due to their ability to rapidly reproduce. The bugs are all female, so they reproduce asexually, only needing a single bug to start a new population.

“There’s research evidence to show that they can have multiple generations per year,” Macy said. “They can go from egg to adult and then lay eggs again within like three weeks.”

How the insects got to the United States and Ohio is a mystery. Macy said he can only speculate, but it’s possible that they came to the U.S. from the shipment of goods. 

“Once it was introduced to North America we don’t know either if it’s being moved around by people accidentally or … the adults are just flying on their own,” Macy said. “There is some research that shows the adult sawflies are pretty strong flyers. They can move potentially 28 to 66 miles in a year. So they are capable of dispersing pretty well on their own.” 

If someone thinks they have found one, Macy encourages them to try to get a clear photo to send to the ODNR Division of Forestry. If possible, collect the bug as well.

“If you can, collect the insect and potentially the leaf that it is on in a bag or a jar or something, to kind of preserve it so we can definitively identify the actual specimen,” Macy said. 

Sightings can be reported to the “Great Lakes EDN” app. Photos and collected specimens can be reported to the ODNR Division of Forestry at 614-265-6694.