For landowners with woodlots or large yards, you can predict next year’s potential level of defoliation by spongy moth (Lymantria dispar) caterpillars by estimating the number of egg masses on your property. The best time to conduct a survey is in fall after trees have dropped their leaves.

To conduct a survey you will need:

• String (18′ 6″) attached to a stake
• Binoculars
• Note pad and pencil
• Map or sketch of the area

1. Select a patch of trees that is representative of the area you are concerned about.
2. Use the stake and string to mark a circle with a radius of 18′ 6″ (this represents 1/40th of an acre).
3. Search within the circle for egg masses. Use the binoculars to look for egg masses high on the trees, especially the undersides of larger branches. Also check all items on the ground such as picnic tables and woodpiles.
4. Write down the number of egg masses and the location of the survey circle.
5. Move at least 150 feet away from your first circle and repeat steps 2 & 3. Space out your survey circles throughout the area you are concerned about.
6. Calculate the average number of egg masses you found in each of your survey circles. An average of greater than 13 egg masses in a residential area or 25 in a woodlot or forest indicates a high likelihood of spongy moth caterpillars causing defoliation in this area. Examine your map to see if there is any pattern to the number of egg masses found. If the number of egg masses increases in one direction, you may want to take more surveys in that direction to determine the extent of the land that could be damaged by spongy moth next year.

Photo Credits: Spongy moth egg mass, Bob Queen, WI DNR. Survey Illustration, Jeanne Gomoll.

The Wiscosnin DNR has a video available here demonstrating this survey method.