The Idaho Department of Lands (IDL) has confirmed the detection of the invasive spongy moth (Lymantria dispar), formerly known as the gypsy moth, in Sandpoint for the second consecutive year. The recent spongy moth captures reflect the first time a potential population has been detected in the Sandpoint area since 1991.
Spongy moth caterpillars feed on a broad range of host trees. The European spongy moth, which prefers broadleaved trees, is established throughout the eastern U.S., where it causes millions of dollars of damage during outbreaks. Spongy moth is NOT established in Idaho, but new introductions can sometimes occur when people accidentally transport insects on firewood, RVs, outdoor gear, or vehicles. Since 1974, state and federal workers have protected the state by placing spongy moth traps throughout Idaho communities every year. The traps allow for rapid detection and eradication of new populations before they become established.
In 2024, one male European spongy moth was detected in a standard monitoring trap in Sandpoint near Oak Street and Division Avenue. In 2025, heavy follow-up trapping, known as delimitation monitoring, was conducted around the initial capture site. Three additional spongy moths were then captured in two delimitation traps in 2025. One trap in a residential tree near Monroe and Poplar captured two moths, and a second trap near the confluence of Syringa Creek and Chuck Slough captured an additional moth. Notably, multiple traps placed between the two capture sites did not capture any moths. The specimens were confirmed as male European spongy moths (L. dispar dispar) via DNA analysis by the USDA Animal and Plant Health Inspection Service (APHIS). Although relevant authorities were notified promptly, initial response planning was delayed due to the federal government shutdown.
The 2025 spongy moth captures are unusual in the history of the Idaho trapping program.
“Over the years, more than 20 similar initial spongy moth detections have occurred throughout many Idaho communities, additional moths have not been caught in any follow-up delimitation trapping since 1994,” said Erika Eidson, IDL Forest Health Specialist. “Often times, initial detections represent a one-off hitchhiker or two, but the subsequent captures in Sandpoint raise questions about a reproducing spongy moth population.”
Follow-up ground surveys conducted in fall 2025 did not find evidence of spongy moth egg masses or visible feeding damage. However, low populations can be very difficult to detect in ground surveys. IDL entomologists estimate the potential population to be very small.
Spongy moths were previously eradicated from Sandpoint and Coeur d’Alene between 1986 and 1991. At the height of that infestation in 1988, more than 300 moths were trapped in Sandpoint. No confirmed detections occurred in the city again until 2024.
Next Steps: Increased Monitoring in 2026
Because the 2025 captures were limited and dispersed, and traps between detection sites were negative, IDL will continue intensive trapping in 2026 to determine whether Sandpoint is threatened by a reproducing spongy moth population. Plans include:
- Placing 50 traps per square mile within 0.5 miles of each positive capture site
- Placing 36 traps per square mile within the 0.5–1 mile surrounding zone
- Mid-season trap checks to ensure any additional moths are detected as soon as possible during the flight season
This approach will help determine whether eradication is truly required and, if so, will help cooperators to define the smallest effective treatment area, evaluate different treatment methods, and conduct timely, appropriate outreach to minimize community impacts.
Spongy moth is a federally regulated pest. Although IDL manages spongy moth monitoring in Sandpoint and other Idaho communities, any necessary eradication response would be coordinated with APHIS and other partners.
What Residents Can Expect in 2026
Residents will see a large number of bright green or bright orange cardboard traps throughout Sandpoint next summer. IDL asks the public not to disturb or remove traps. Vandalism and removal will reduce the effectiveness of early-detection efforts.
For questions about the detections or the 2026 monitoring plan, please contact the Idaho Department of Lands.
Stop the Spread of Invasives Insects
To 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.
