Stonefly Species Skwala americana (Large Springflies)

Head color pattern as shown in Figure 7. All pale areas conspicuously yellow. Transverse pale M-line very conspicuous. Tentorial rugosities yellow. Large yellow crown patch joined to extensive yellow region of the occiput. No dark brown color behind the compound eyes. Forewing length 5–6 mm.

Ninth abdominal segment very slightly emarginate above and without spinulae. Tenth segment widely split above; dorsal lobes small, thumb-like, and bearing several spinulae. Supraanal process largely imbedded in membrane, and its lateral styles not visible when not extruded. When extruded, the supra-anal process shows as a well sclerotized, nearly cylindrical process, membranous and somewhat bilobed at the tip. Lateral styles small but well sclerotized; the free part tapers rapidly and curves slightly inward to its sharply pointed apex. The membranous region between the lateral stylets and the base of the supra-anal process is thickly beset with a mat of very fine hairs. See Frison, 1936, for accurate figures of the male of this species.

Head color pattern as shown in Figure 7. All pale areas conspicuously yellow. Transverse pale M-line very conspicuous. Tentorial rugosities yellow. Large yellow crown patch joined to extensive yellow region of the occiput. No dark brown color behind the compound eyes. Forewing length 5–6 mm.

Forewing length 12–15 mm. Subgenital plate protrudes only slightly over segment nine; with a very broad apical emargination. See Frison, 1937, for figure of subgenital plate (shown under the defunct name Hydroperla parallela).