Emerging aquatic insects can transport beneficial nutrients and harmful contaminants accumulated during aquatic life stages to terrestrial food webs. Contrasting the beneficial “bright” and harmful “dark” sides of aquatic insect fluxes between habitats of different productivity can improve understanding of how aquatic ecosystem stressors such as eutrophication may affect their net benefits and costs to recipient consumers. We quantified the seasonal (wet and dry) fluxes of the essential fatty acid eicosapentaenoic acid (EPA; 20:5n-3) and the neurotoxin methylmercury (MeHg) from emerging aquatic insects in an oligotrophic and a eutrophic freshwater marsh of the subtropical Florida Everglades. To assess potential consequences for terrestrial insectivores, we also quantified EPA and MeHg availability in above-water invertebrates inhabiting emergent vegetation. EPA flux was 241X greater in the eutrophic habitat across both seasons but varied seasonally within each habitat. In the eutrophic habitat, the wet season EPA flux was 2.3X greater than in the dry season and in the oligotrophic habitat, the dry season EPA flux was 13.7X greater than in the wet season. The MeHg flux did not differ between habitats but was 4.7X greater in the dry season. Patterns of EPA and MeHg availability in above-water invertebrates mirrored emerging insect fluxes, indicating that aquatic export directly translated into availability for terrestrial insectivores. Spiders (Araneidae, Tetragnathidae, Philodromidae, Pisauridae, and Salticidae) and adult damselflies (Zygoptera) dominated the MeHg and EPA availability in both habitats. These findings suggest that wetland trophic status is linked to the quantity and quality of emerging aquatic insect subsidies, potentially enhancing EPA availability for terrestrial insectivores without increasing MeHg exposure. This study also illustrates that variation in aquatic ecosystem productivity can decouple EPA and MeHg dynamics in linked aquatic-terrestrial food webs.