Community structure and biomass of aerial insects in different habitats of the upper Llano River watershed (Texas, USA)

Riparian ecosystems in semi-arid regions function as biodiversity hotspots, where seasonal pulses of aquatic insect emergence subsidize terrestrial food webs and influence foraging ecology and recruitment for insectivorous vertebrates. To evaluate the biomass and community composition of aerial invertebrates as potential prey for Rio Grande Wild Turkeys (Meleagris gallopavo intermedia) and other predators, I conducted a two-year study (2023-2024) in the Upper Llano River Watershed, Kimble County, Texas. Using cylindrical sticky traps deployed in paired riparian and upland habitats across five study sites along the South Llano and North Llano rivers, I quantified biomass, diversity, composition, and body size of aerial invertebrates. Across 480 traps, I collected 7,478 aerial invertebrates ≥4mm in length, representing 14 orders and 111 families. Terrestrial taxa made up the majority of the invertebrate biomass collected in both habitats and sample years (>85%), while aquatic insects contributed approximately 10 – 15% of biomass. The aquatic insects exhibited seasonal pulses in biomass, with mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera) all peaking in late spring. Hexagenia spp. showed the most pronounced emergences of all the aquatic taxa represented. Biomass declined in 2024, highlighting interannual changes as a key driver of invertebrate availability. Repeated-measures ANOVAs confirmed that time and origin were the most consistent significant effect for the changes in biomass during both sampling seasons. Additionally, non-metric multidimensional scaling and the associated ANOSIM results further confirmed that interannual turnover was the dominant structuring factor at both the order and family levels. Body size analyses demonstrated that aquatic invertebrates were significantly larger than terrestrial taxa (mean 7.56 vs. 6.53 mm; p < 0.001), underscoring their potential value as high-quality and visually conspicuous prey. Together, these results establish baseline information of aerial invertebrate emergence timing and biomass composition in the Edwards Plateau Ecoregion of Texas. For aerial insectivores like barn swallows, purple martins, and potentially terrestrial predators like Rio Grande Wild Turkeys, seasonal pulses of aquatic insects provide critical food subsidies that align with nesting and brood-rearing.