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Family Capniidae - Small Winter Stoneflies

Stonefly - Allocapnia nivicola - male Small Winter Stonefly - Allocapnia pygmaea - female Small Winter Stonefly - Paracapnia Stonefly Capniidae, genus Allocapnia - Allocapnia Small Winter Stonefly Stonefly Allocapnia pygmaea - male
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Plecoptera (Stoneflies)
Superfamily Nemouroidea
Family Capniidae (Small Winter Stoneflies)
Other Common Names
Snowflies
Numbers
>160 spp. in 10 genera in our area(1), almost 300 spp. in 17 genera worldwide(2)
Size
adult length usually <10 mm (average ~7 mm)
Identification
Adult: blackish or dark brown with reduced wing venation; forewing has few cross veins, and cells are elongate, of different sizes, and not arranged in rows; wings of some males are short or rudimentary; in Allocapnia, anal lobe of hindwing is nearly as long as rest of wing, whereas in Capnia, anal area reaches not more than half length of wing; cerci longer than greatest width of pronotum
Nymphs: slender, brown or blackish with no thoracic or abdominal gills; hindwing pads nearly parallel to body; dorsal and ventral halves of abdominal segments 1-9 divided laterally by membranous fold; second tarsal segment much shorter than first (a feature shared with nymphs and adults of Nemouridae and Leuctridae); 3 ocelli
Range
holarctic(2); much of NA, many species are restricted to relatively small areas
Habitat
nymphs beneath rocks and gravel on the bottom of streams and rivers; adults often seen on snow, or resting on concrete bridges over streams
Season
adults emerge from November to June (most common in winter and early spring)
Food
nymphs feed on aquatic plant material, adults feed on blue-green algae
See Also
Adult Leuctridae are very similar but forewings at rest are bent down over sides of abdomen, most species have a western distribution, and are not present in winter. Nymphs of Leuctridae have only abdominal segments 1-7 (or less) divided by membranous lateral fold.
Adult Taeniopterygidae have two adjacent rows of broad rectangular cells of similar size (resembling rungs of a ladder) near base of forewing, and second tarsal segment is about as long as first in nymphs and adults.
Internet References
Family overview by C.R. Nelson (Tree of Life)