In spite of Illinois' seemingly endless cornfields (formerly prairies), which occupy much of the central parts of the state, we are fortunate to have several hundred caves in four of Illinois' five karst regions along the southern, western, and northwestern borders of the state. Nearly all of our caves have developed in limestone bedrock. (Map courtesy of C. Pius Weibel and Samuel V. Panno, Illinois State Geological Survey - see literature section below for complete map citation.)
Within caves a diverse biota may be found, exhibiting varying degrees of adaptation to the subterranean environment. Accidental species, which fall, wander, or are washed into caves, do not linger long in this environment. These animals either return to the surface, or die in the caves - where they provide an important source of nutrients for the cave community. Trogloxenes occur commonly in caves, but must leave the cave at some point in their life cycle, typically for feeding. Species which occur in caves and can complete their entire life cycle there, but which are also found in similar habitats above ground, are referred to as troglophiles. And finally, troglobites are those species which are obligate cave dwellers adapted so completely to caves that they are restricted to this environment. To confuse matters further, the current trend is to use the prefix 'troglo' with reference only to terrestrial fauna, and the prefix 'stygo' for aquatic species. Thus, for aquatic species, trogloxene becomes stygoxene, troglophile becomes stygophile, and troglobite becomes stygobite.
Two other common groupings of cave inhabitiing animals are edaphobites, obligate deep-soil dwellers which may occur in caves, and phreatobites, obligate groundwater inhabiting species - most often envisioned as species found in slower moving, interstitial groundwater. [Top of Page]
Because of the extreme isolation, uniqueness, and harsh conditions of the cave environment, many of the species which occur here, especially obligate cavernicoles, are rare. Several merit threatened or endangered species status at the state or federal level, or are endemic to (restricted to) a small geographic area.
The cave environment varies as one moves farther away from the land above. This environmental variation has been used to classify parts of the cave into ecological zones. The entrance zone is similar to the environment above ground, varying greatly in temperature and humidity. This zone receives ample sunlight, and green plants, often species adapted to cool, moist microhabitats, are present. In the twilight zone, a little farther into the cave, available light is greatly reduced, and thus plants are no longer able to grow. The temperature is somewhat buffered by the cave environment, but temperature and humidity still vary with fluctuations in surface weather. This dimly light zone is home to a mix of surface animals (e.g., trogloxenes, stygoxenes, and accidentals) as well as cave adapted species. The entrance and twilight zones are sometimes referred to collectively as the threshold zone. Still farther into the cave, we enter the middle zone, where we first encounter complete darkness. This zone still experiences some temperature and humidity fluctuations in response to surface weather changes. In the larger caves, there is one final zone, the dark zone. This part of the cave is characterized by constant temperatures (54-56 °F in Illinois) and humidity. This part of the cave is home to an array of unusual troglobites and stygobites. Some authors refer to the middle and dark zones collectively as the dark zone, which is then subdivided into the variable-temperature dark zone (=middle zone, above) and the constant-temperature dark zone (=dark zone, above).
A variety of habitats, both terrestrial and aquatic, are found in Illinois caves. Terrestrial habitats are often damp, but a few Illinois caves, especially those with large entrances that face the west, may be very dry. Typical terrestrial habitats include flood debris (including logs, twigs and leaves from the surface), animal feces (often from raccoons or bats) clay floors, rocky floors, and bedrock walls and ceilings. The predominant aquatic habitats in Illinois are found in cave streams. Streams typically include shallow, fast flowing rocky sections, riffles, and slower moving, often silt-bottomed pools. Different animal species are dominant in these different parts of the stream. Drip pools, sometimes found beneath active formations away from the cave stream, are another kind of aquatic habitat, where species typically found in narrow spaces in the bedrock and soil above may sometimes be found.
The diversity of vertebrate animals in caves is not nearly as great as that of the invertebrates. In Illinois, vertebrates commonly found in caves include the Eastern Phoebe (Sayornis phoebe) - a species which builds a mossy nest on the bedrock walls of cave entrances; the Raccoon (Procyon lotor) - seldom seen in the caves, but evidenced by its feces; salamanders (including the cave salamander [Eurycea lucifuga], the long-tailed salamander [Eurycea longicauda], and the slimy salamander [Plethodon glutinosus]) which are most commonly found in the entrance and twilight zones of our caves, but are sometimes found far from any entrance; frogs (such as the pickerel frog, Rana palustris) which are sometimes common winter inhabitants of the entrance and twilight zones; and finally, Bats. Many species of bats are well adapted for cave life, but they must return to the surface to feed. Some bats commonly found in Illinois caves include the eastern pipistrell (Pipistrellus subflavus), the little brown bat (Myotis lucifugus), the big brown bat (Eptesicus fuscus) and two federally endangered species, the Indiana bat (Myotis sodalis), and the gray bat (Myotis grisescens) (learn more about the gray bat from the U.S. Fish and Wildlife Service). Several Illinois bats are threatened or endangered at the state level.
The invertebrates found in caves form an unusual and diverse assemblage of creatures, including snails, flatworms, spiders, springtails, cave crickets, millipedes, flies, aquatic isopods, amphipods, and beetles. Some of these species are slow moving, pale in coloration, blind, and bear long appendages - these are the stygobites and troglobites, adapted for life underground. Pictures of some of these animals can be found on my cave critter picture page.
Ahrens-Voelker, K. 1997. Illinois' land of 10,000 sinkholes. Illinois Audubon 262(Fall 1997):15-18.
Aley, Thomas. 1998. An Editorial: The Illinois Cave Amphipod; a collection of classical problems. American Caves 11(1):8-11.
Aley, Thomas; Philip Moss, and Catherine Aley. 2000. Delineation of recharge areas for four biologically significant caves in Monroe and St. Clair Counties, Illinois. An unpublished Ozark Underground Laboratory report to the Illinois Nature Preserves Commission and the Monroe County Soil and Water Conservation District. 254 p. + appendices and maps.
Allen, J. 1999. To the Bat Cave, Robin! Abandoned mines in LaSalle County provide the perfect habitat for hibernating bats. Outdoor Illinois, April 14-17.
Boehm, S. and P. Moss. 1997. Our secret underworld. Illinois Audubon 262(Fall 1997):4-9.
Gardner, J. E., S. J. Taylor and J. Krejca. 1992. Cave Dwellers. Illinois Natural History Survey Reports No. 318:2-3.
Herkert, J. R. (ed.). 1992. Endangered and Threatened Species of Illinois: Status and Distribution, Volume 2 - Animals. Illinois Endangered Species Protection Board, Springfield, Illinois. 142 pp.
Herkert, J. R. 1994. Endangered and Threatened Species of Illinois: Status and Distribution, Volume 3 - 1994 Changes to the Illinois List of Endangered and Threatened Species. Illinois Endangered Species Protection Board, Springfield, Illinois. 33 pp.
Korab, H. 1999. Goundwater protection in karst areas. The Illinois Steward 8(2):19-24.
Krohe, J., Jr. 1999. The Sinkhole Plain: An Inventory of the Region's Resources. Illinois Department of Natural Resources, Office of Realty and Environmental Planning. 22 pp.
Oliver, J. S. and R. W. Graham. 1988. Preliminary inventory of natural resources in select caves in Illinois. Illinois State Museum, Springfield, Illinois. viii + 115 pp.
Panno, S. V., K. C. Hackley, W. R. Kelly and H. H. Hwang. Sources of nitrate contamination in karst springs using isotopic chemical and bacterial indicators: preliminary results. In: Proceedings of the Illinois Groundwater Consortiums' Ninth Annual Conference - Research on Agricultural Chemicals in Illinois Groundwater (1 April 1999). 10 pages.
Panno, S. V., I. G. Krapac, C. P. Weibel, and J. D. Bade. 1996. Groundwater contamination in karst terrain of southwestern Illinois. Illinois State Geological Survey Environmental Series Report 151. Champaign, Illinois. 43 pp.
Panno, S. V., C. P. Weibel, C. M. Wicks, and J. E. Vandike. 1999. Geology, hydrology, and water quality of the karst regions of southwestern Illinois and southeastern Missouor. Geological field Trip @: April 24-25, 1999. Illinois State Geological Survey, ISGS Guidebook 27. 33rd Annual Meeting of the North-Central Section of the Geological Society of America. 38 pp.
Peck, S. B. and K. Christiansen. 1990. Evolution and zoogeography of the invertebrate cave faunas of the Driftless Area of the Upper Mississippi River Valley of Iowa, Minnesota, Wisconsin, and Illinois, U.S.A. Canadian Journal of Zoology 68:73-88.
Peck, S. B. and J. J. Lewis. 1978. Zoogeography and evolution of the subterranean invertebrate faunas of Illinois and southeastern Missouri. NSS [National Speleological Society] Bulletin 40(2):39-63.
Taylor, S. J. and D. W. Webb. 1998. The fragile fauna of Illinois caves. The Illinois Steward 7(2):2-6. ([web version] [lacks photo credits])
Taylor, S. J. and D. W. Webb. 2000. Human impacts on groundwater quality and subterranean aquatic biota in southwestern Illinois. Illinois Natural History Survey
Reports No. 361:2-3.
Toomey, R. S. 1997. Living in the dark. Illinois Audubon 262(Fall 1997):10-14.
U.S. Department of the Interior. 1998. Endangered and Threatened Wildlife and Plants; Final Rule To List the Illinois Cave Amphipod as Endangered. Federal Register 63(171):46900-46910.
U.S. Fish and Wildlife Service. 2002. Illinois Cave Amphipod (Gammarus acherondytes) Recovery Plan. U.S. Fish and Wildlife Service, Ft. Snelling, Minnesota. vi + 63 p.
Webb, D. W., S. J. Taylor, and J. K. Krejca. 1994. The Biological Resources of Illinois' Caves and Other Subterranean Environments. Technical Report 1993 (8), Illinois Natural History Survey, Center for Biodiversity. Illinois Department of Energy and Natural Resources ILENR/RE-EH-94/06. 168 pages.
Wetzel, M. J. and S. J. Taylor. 2001. First records of freshwater oligochaetes (Annelida, Clitellata) from caves in Illinois and Missouri, USA. Journal of Cave and Karst Studies 63(3):99-104.
Note: Dead links removed: Dec 2001, Sept 2003, Oct 2009 - if you know a link that should be here, let me know!
Subterranean Ecology Institute, Inc.
Other cave-related sites in the region:
Little Egypt Grotto (Carbondale, IL)
Other cave sites:
INHS research projects focusing on cave fauna have included several topics:
● The Illinois Cave Amphipod, which is listed as endangered by the USFWS under the federal endangered species act. Some of my work on this species has been in collaboration with Frank Wilhelm when he was at Southern Illinois University at Carbonale.
Critical to several of these studies is the examination of groundwater quality. The potential for groundwater contamination comes from sedimentation (associated with row crop cultivation, overgrazing/overutilization by livestock, and by urbanization or other developmwnt), agricultural chemicals (primarily springtime herbicide applications on row crops), waste water (originating from inadequate treatement of human sewage or from livestock waste), visitation (by well trained cave visitors as well as vandals), runoff from highways (oil and gas from normal traffic, road salts in the winter), landfills (when inadequately sealed and inapropriately placed in a karst terrain), and the possibility of other spills (such as tanker trucks overturning and leaking into sinkholes, gas station tank leaks, and other hazardous fluid storage unit failures). All of these potential contamination sources are associated with aspects of modern culture which society views as necessary. Therefore, we cannot simply eliminate the contamination sources, but must work closely with individual residents and local and regional governments to try to find viable solutions to these complex, long term conservation and management problems.
Created 4 December 1997, last modified 9 May 2011.