In 2024, the Wisconsin Spongy Moth Program set 8,921 traps in 44 counties spanning from central to western Wisconsin.
Preliminary data shows the estimated total of statewide male spongy moth catches this year is 213,623. This is approximately half as many moths as were caught last year. The majority of these trap catches were recorded in the central and eastern parts of the state that have historically experienced spongy moth infestations.
This year’s decrease indicates the first relief from an outbreak that had been building since an exceptionally low population in 2019 and peaked with record-high moth catches in 2023. Such outbreaks typically occur every 10 years in areas where spongy moth is established and usually persist for two to four consecutive years before populations collapse.
The unusually wet spring, combined with large caterpillar populations, provided the right conditions for widespread caterpillar mortality in 2024 due to naturally occurring fungal and virus controls.
Follow-up egg mass surveys are scheduled for fall 2024 to help determine whether unusually high trap counts in historically uninfested areas reflect the westward spread of persistent populations or rather a spillover of transient male moths from more heavily infested areas to the east.
Pictured below: 2024 Spongy Moth Trap Catches. Photo by DATCP’s A. Miller
