RES Handbook Vol 1 Part 6. Plecoptera

RATHER weakly chitinized insects with two pairs of membranous wings often reduced in the male. Antennae filiform, long, mouth-parts of biting type. Legs with only three tarsal segments. Abdomen terminating in a pair of jointed cerci, which may be reduced to one or two segments. Male genitalia diverse in form, differing considerably in the different genera. In the female, the VII, VIII or IX sternite may be modified to form a sub- genital plate. In some families, vestiges of the nymphal gills persist in the imagines. Certain genera of LEUCTRIDAE and NEMOURIDAE show a decided tendency to brachyptery and reduced size in both sexes at altitudes over 1000 ft.