Family Capniidae - Small Winter Stoneflies

Snowflies

For consistency, the common names of families used in Peterson's Field Guide (1) are followed in BugGuide, with names proposed by Stark et al given as alternates.

151 species in 10 genera (nearctica.com)

adult length usually under 10 mm (average about 7 mm)

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

family is distributed throughout much of North America but many species have restricted geographic ranges, and are endemic to relatively small areas

nymphs live beneath rocks and gravel on the bottom of streams and rivers

adults are often seen on snow, or resting on concrete bridges over streams

adults emerge from November to June (most common in winter and early spring)

nymphs feed on aquatic plant material

adults feed on blue-green algae

Adult Rolled-winged Stoneflies (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 Winter Stoneflies (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.

Stark, B.P., K.W. Stewart, S.W. Szczytko, and R.W. Baumann. 1998. Common Names of Stoneflies (Plecoptera) from the United States and Canada. Ohio Biological Survey Notes 1:1-18.

live adult and nymph images of Capnia species by C. Riley Nelson, plus classification, phylogeny, description, habitat, distribution, references (Tree of Life, U. of Arizona)

nymph images showing membranous fold on abdomen (Govt. of California)

US distribution maps and common names of most species in North America (Capniidae, Stoneflies of United States; USGS)

common name reference [Small Winter Stoneflies] (U. of Georgia)

common name reference [Snowflies] (Pennsylvania State U.)