Ohio says to beware the elm zigzag sawfly

• They've been spotted in Canada and eastern U.S. states in recent years.

Why it matters: These unwelcome guests are "capable of significant defoliation of elm trees," ODNR notes.

Threat level: While they're not known to cause trees' death, their full impact on tree health is not entirely known.

What they're saying: Kathleen Knight, a U.S. Forest Service research ecologist, tells Axios it's unclear how the sawflies got here.

• "Humans are pretty efficient at moving things around accidentally, so it's possible they were brought into Ohio by people inadvertently."

Zoom in: The light-green larvae are up to one-half-inch long and leave a distinctive pattern on leaves, hence their name.

• Adult elm zigzag sawflies are smaller, shiny black in color and have wings.

How you can help: Report sightings and infestation patterns on the Great Lakes Early Detection Network phone app or call ODNR's Division of Forestry at 614-265-6694.

• You're encouraged to take photos or collect the insect specimen.