invertebrates on organic debris in a large Illinois cave. Photo (c) Steve Taylor
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invertebrates on organic debris in a large Illinois cave. Photo (c) Steve Taylor |
Special Note:In order to facilitate faster loading of this page, I have moved all of my cave critter pictures to a cave critter picture page. [Top of Page] 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.) [Top of Page] 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] Threatened and Endangered Species
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. [Top of Page]
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Cave Zones 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). [Top of Page] 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. [Top of Page]
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.
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One of the most extreme examples of this phenomenon in Illinois is the 'Illinois Cave Amphipod,' Gammarus acherondytes Hubricht and Makin,
which is known from only six caves, all within about 10 miles of one another. Illinois lists this species as being state endangered, and it recently has been 
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 
Two documents help provide some legal protection for our cave resources. These are 