The NSS Bulletin - ISSN 1090-6924
Volume 40 Number 2: 39-63 - April 1978

A publication of the National Speleological Society

Zoogeography and Evolution of the Subterranean Invertebrate Faunas of Illinois and Southeastern Missouri
Stewart B. Peck and Julian J. Lewis


Some 215 species of invertebrates, excluding accidentals and parasites, are known to occur in cave and groundwater habitats in Illinois [excluding the Driftless Area] and adjacent Missouri counties bordering the Mississippi River. Forty-three of these species are troglobites or phreatobites, of which 24 are aquatic and 19 are terrestrial.

This troglobite-phreatobite category includes three flatworms, three snails, one copepod, eight aquatic isopods, nine amphipods, two pseudoscropions, one spider, five millipeds, four collembolans, three dipluran, and four beetles. The terrestrial species have generally smaller distributional ranges than do the aquatics. Some members of the cave community are pre-Pleistocene relicts, and some may represent early-Pleistocene invasions of subterranean habitats. Most of the fauna has been derived from eastern (Appalachian) sources. Because Illinois and nearby Missouri caves were probably uninhabitable (because of the nearness of glacial ice) during the Illinoian glacial maximun, the local fauna represents a post-Illinoian (early Sangamonian) occupation of the caves. Warm-dry middle Sangamonian climates caused the genetic isolation of some pre-adapted epigean invertebrate populations in caves, and some of these survived to become cave-adapted troglobites. At its maximum, Wisconsinan glacial ice came within 100 miles of part of the cave area. Cool-moist Wisconsianan climatic conditions allowed the overland dispersal of terrestial troglobites through deep moss and litter carpets, and the subteranean-interstitial dispersal of most aquatic troglobites. Through this Wisconsinan disperal, the species attained much of their modern distribution. Recent climatic warming-drying has caused the limitation of these species to their present day cave and groundwater localities. interstitial distribution of phreatobites northward along major valleys into glacial drift plains has been extensive in the post-Wisconsinan.

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