Aquatic insect functional feeding groups (FFGs) were defined in the seminal paper on trophic relations of aquatic insects by Cummins (1973). While FFGs are useful for understanding generalized feeding behaviors of insects, they can sometimes misrepresent the true diversity of feeding habits within functional groups. For example, previous work has suggested that the free-living trichopteran, Rhycacophila, which are characterized as predators during the larval stage, have species that may feed as omnivores or herbivores, in addition to those species that feed as predators. Ingested diets can also vary at the individual level, within species, based on site location or season, suggesting opportunistic feeding behavior. Furthermore, ingested items do not always reflect assimilated resources that support aquatic insect production, which means that FFG classifications alone may not provide information about energetic support of insect consumers. Therefore, we asked: (1) do the ingested diets of aquatic insects conform to FFG classifications, and (2) how do ingested diets of aquatic insects compare to estimates of assimilated resources inferred using stable isotope analysis? We collected insect taxa representing 9 families and 14 genera from Sucker Brook, a forested headwater stream in the Adirondack Park(New York, USA). For each individual collected, we conducted gut content analysis (GCA) to compare their ingested diets to assigned FFGs and stable isotope analysis (d13C and d15N) to compare assimilated energy toingested diets. GCA involved dissection of specimens, filtration of gut contents, and identification and enumeration of food particles (i.e., diatoms, amorphous detritus, cyanobacteria, animal prey, and filamentous algae)using ImageJ. Preliminary results suggest that individual gut contents largely reflect the food habits of their FFG, but some unexpected diet items were observed across all functional groups. Next, we will use stable isotope analysis (SIA) to determine assimilated diet components, which we will compare with GCA results to understand the relationship between ingested diet items and assimilated resources. Our research advancesunderstanding of the cryptic ecologies of aquatic insect taxa and provides new insights into the relationship between ingestion and assimilation of resources in stream food webs.