The Winter Stoneflies of Illinois (Insecta: Plecoptera)

100 Years of Change

Abstract

Winter stoneflies (Insecta: Plecoptera) are an aquatic group of insects whose adults emerge in IIlinois from late November to early April. Twenty-one species have been reported from Illinois. Extensive collections of winter stoneflies were made in Illinois during the 1920s and 1930s by Frison, the 1960s by Ross and “the winter stonefly club’, and the 1990s by Webb. These specimens are housed in the Insect Collection of the Illinois Natural History Survey and allowed for an evaluation of the current status of these species following a century of environmental change.
Over the past century (1900-2000), the species diversity of winter stoneflies averaged 2.5 species per county with species reported from every county but 3 (Carroll, DuPage, Ford) and with 10 counties recording 5 or more species. Pope County (13 species) reported the greatest species diversity. During the recent resurvey (1976-2000), species diversity average 1.9 species per county with
specimens not collected in 11 counties, and only 3 counties (Hardin, Pope, and Saline) exhibited 5 or more species.
Four species are considered extirpated from Illinois: Allocapnia illinoensis, Nemocapnia carolina, Paracapnia angulata, and Taeniopteryx parvula. Seven species were found to be common (known from more than 15 localities): Allocapnia forbesi, A. granulata, A. mystica, A. rickeri, A. vivipara, Taeniopteryx burksi, and T: nivalis. Four species are considered uncommon (known from 4—15
localities): Allocapnia recta, Strophopteryx fasciata, Taeniopteryx metequi and Zealeuctra claasseni. Six species are considered rare (known from 1-3 localities): Allocapnia nivicola, A. smithi, Prostoia completa, Taeniopteryx lita, Zealeuctra fraxina, and Z. narfi. Significantly reduced patterns of distribution were noted in three species: A. granulata, A. mystica, and Strophopteryx fasciata. Only
Taeniopteryx nivalis, previously rare, is now spreading its distribution across northern Illinois.
There has been a modest decline during the past century in the diversity of stonefly species within various counties. Also, a trend was observed toward an increase in pollution-tolerant, “generalist” species with a decrease in pollution-sensitive, habitat “specialists.”