 Planned area of spongy moth delimitation trapping in Sandpoint for 2025. The yellow cross represents the location of the 2024 capture of a single male spongy moth. The surrounding grid represents planned delimitation traps for 2025, placed at a density of 36 traps per square mile in the four square miles surrounding the capture site. Only approximate trapping locations are shown. Some cells may not be able to be trapped due to lack of access or permission on private property. Traps will be placed in the public right of way as much as possible, or on private property with permission from the landowner. Trap placement, checks, and removal will be conducted by the Idaho Department of Lands. This intensive delimitation trapping will help outline the possible extent and severity of the infestation while also reducing the local moth population. Map by the Idaho Department of Lands.
About the European spongy moth (Lymantria dispar dispar): This type was introduced into the eastern US in 1869 and is now established in about 20 northeastern and midwestern states. European spongy moth feeds on the leaves of various broadleaved trees and shrubs, particularly oak trees. Outbreaks can lead to significant damage, costing millions of dollars. European spongy moth has limited dispersal capabilities because the female moths cannot fly, so new introductions are often caused by humans moving infested materials to new locations.
Preventing the establishment of spongy moth populations: Since its inception in 1974, the Idaho spongy moth trapping program has captured spongy moths in many Idaho cities and has successfully eradicated spongy moth from the state multiple times. The last time spongy moths were captured in Sandpoint was between 1986 and 1990. At the peak, 334 moths were captured in Sandpoint in 1988. The population was successfully eradicated by 1991. Traps are placed in Sandpoint every year at a density of one trap per square mile, and no additional spongy moths have been captured in Sandpoint until this year.
Next steps: A single moth capture does not usually lead to an established population that requires eradication. The next step is to determine whether this incident was a one-off occurrence or if it signifies the beginning of a breeding population. To investigate this, IDL will conduct delimitation trapping in 2025. This will involve placing 36 traps per square mile across the four square miles surrounding the capture site (covering all of the downtown area of Sandpoint). If additional moths are present, this intensive trapping will help outline the extent and severity of the infestation while also reducing the local moth population.
What to look for: Residents can expect to see numerous bright green or bright orange cardboard traps throughout Sandpoint in the summer of 2025. It is crucial to leave these traps undisturbed to allow for proper monitoring by the Idaho Department of Lands. Removing or vandalizing the traps can hinder data collection on the potential spongy moth population.
 Spongy moth monitoring trap. If you see a trap like this, please leave it alone and call the number listed on the trap with any questions or concerns. Photo by Idaho Department of Lands.
"Although capturing an invasive insect is never good news, the Idaho spongy moth trapping program is working as designed to help keep this damaging and expensive pest out of Idaho," said Erika Eidson, Forest Health Specialist with the Idaho Department of Lands. "We detected this new introduction quickly. Early detection lowers the need for costly, large-scale pest management and improves eradication outcomes."
Help prevent the spread of spongy moth and other invasive insects: Avoid moving firewood long distances (buy it where you burn it), check outdoor objects for signs of insects before relocating them, and report any suspicious sightings or tree damage to the Idaho Department of Lands.
Name change: The spongy moth was formerly known as the gypsy moth (a name changed by the Entomological Society of America in 2021). The new name reflects its spongy egg masses, aligning with the French common name for the species (spongieuse).
Learn more about forest health and insect detection: https://www.idl.idaho.gov/about-forestry/forest-health/
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