The Capniidae, the small winter stoneflies, are a family of insects in the stonefly order (Plecoptera). It constitutes one of the largest stonefly families, containing some 300 species distributed throughout the holarctic. Their closest relatives are the rolled-winged stoneflies (Leuctridae).

Many species are endemic to small ranges, perhaps due to the family's tendency to evolve tolerance for cold (isolating populations in mountain valleys) and winglessness (inhibiting dispersal). Indeed, some wingless Capniidae – e.g. the Lake Tahoe benthic stonefly ("Capnia" lacustra, Capnia is not monophyletic and this species is suspected to belong elsewhere) or Baikaloperla spp. – spend their entire lifecycles under water and do not disperse from their native lakes at all.

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