Goodyear Swamp Sanctuary, a wetland adjacent to Otsego Lake, Otsego County, New York, has been dominated by the invasive nonnative plant purple loosestrife (Lythrum salicaria L.) since 1975. In June 1997 a combined total of 100 adult Galerucella calmariensis (L.) and G. pusilla (Duft) were introduced into the Sanctuary in an attempt to control loosestrife. Since then, annual spring and fall monitoring has been conducted on 5/m² quadrats with the intention of evaluating the abundance of Galerucella spp. and their impact on loosestrife over time. Through 2000 Galerucella spp. populations increased, as did damage to loosestrife, though not to the extent of controlling its growth or seed production. During the summers of 2001 and 2002 loosestrife was decimated. Following those periods, ephemeral non-target feeding by Galerucella spp. was documented primarily on red osier (Cornus stolonifera) in 2001 and speckled alder (Alnus rugosa) in 2002 with three other species being grazed to a lesser degree. No non-target species were substantially impacted during these brief periods (<1 wk). Temporal variation in the population distribution suggests that a shortage of appropriate food may have initiated early aestivation. During the summer of 2002 Galerucella spp. were found 9 km off-site, believed to result from a single-season dispersal, suggesting a mobility of a greater extent than previously recorded.