Aquatic invertebrates provide protein-rich foods for dabbling ducks (Anatini) and other waterfowl throughout their annual cycle. During winter, some species (e.g., mallard [Anas platyrhynchos]) undergo molt and acquire body reserves for migration and egg formation, which increase protein demands met primarily through consumption of invertebrates. Habitat managers often flood unharvested agricultural crops to increase energetic carrying capacity for waterfowl. However, few studies have estimated abundance of invertebrates in flooded croplands. In Mississippi in January 2009, we used a sweep net to sample invertebrates in three flooded corn fields containing a dense understory of moist-soil grasses and sedges (i.e., grassy corn), three adjacent moist-soil wetlands, two wetlands with robust (≥1 m) moist-soil vegetation, and two stands of flooded bottomland hardwood forest. Invertebrate dry mass in moist-soil wetlands (x¯ = 0.048 kg ha-1) was 1.7 times greater than in adjacent grassy corn (x¯ = 0.029 kg ha-1); however, both contained less biomass of invertebrates than robust moist-soil (x¯ = 2.35 kg ha-1) and forested wetlands (x¯ = 7.39 kg ha-1). Our study provides preliminary estimates of invertebrate biomass in flooded grassy corn compared with other nearby wetlands managed for waterfowl, but replication is needed to estimate invertebrate resources in these wetlands at the scale of the Mississippi Alluvial Valley. We suggest managing grassy corn to increase energy availability for waterfowl, but also encourage habitat managers to provide forested, moist-soil, and other wetlands in winter habitat complexes to increase invertebrate resources.