Adults of brown lacewings (Hemerobiidae) and green lacewings (Chrysopidae) are reliably distinguished by costal crossveins, the veins perpendicular to wing length and just below the upper (costal) edge of front wings. In green lacewings, such as Chrysopa and Chrysoperla spp., the costal crossveins are not forked (bifurcate, or Y-shaped). In brown lacewings, such as Hemerobius spp., many or all costal crossveins fork.
Photo by Serediuk HV. 2018. Morphometry of Fore Wing Venation for Identification of Net-winged Insects. Vestnik Zoologii 52(2):101-114. Brown lacewing from Nakahara W. 1960. Systematic Studies of the Hemerobiidae (Neuroptera). Mushi 34(1):30.