Rock Island Ecological Services Office
Midwest Region


Gammarus acherondytes

Photography by the Illinois Natural History Survey


The Illinois Cave Amphipod was listed as an endangered species on September 3, 1998. The Service has recently formed a Recovery Team which held its initial meeting on April 8, 1999.


This report is a compilation of information on the species and its habitat from published and unpublished literature, as well as the opinions of experts on the species and the threats to its continued existence. The following paragraphs summarize the most important information contained in the available data. (Contact the author: Gerry Bade)

Description: Amphipods are members of the phylum Arthropoda ("jointed foot"), subphylum Crustacea. They resemble small, tailless shrimp with laterally flattened bodies. Most amphipods are small and live in marine environments. Illinois cave amphipod males are up to 20 millimeters (0.8 inches) long; females are up to 16 millimeters (0.6 inches) long. They are light blue-gray and nearly eyeless.

This species occurs only in underground streams. It was first collected in 1938 and described as a new species in 1940. It has only been found in six cave streams in the southwestern Illinois counties of St. Clair and Monroe. These caves all lie within a 10-mile radius circle around Waterloo, Illinois, making this a very localized species. However, there is no evidence that these cave streams are currently interconnected.

Population Trends: Small, aquatic, cave animals are very difficult to locate, capture, and identify. The number of animals found during successive surveys may vary greatly depending upon the experience of the observer; water temperature, turbidity, and velocity; time of the year; accessibility of the smaller channels within the cave; the amount of time spent in the cave; and local rainfall events during the previous several days. Thus, because statistically valid population estimates are nearly impossible to acquire, the number of known populations and the threats to them become the primary indicators of the "health" of such species.

The Illinois cave amphipod was discovered in two caves in 1940. A third cave was found to contain the species in 1965 and two more caves were added to the list of Illinois cave amphipod sites in 1972. In 1986 a single specimen of the species was collected from a sixth cave. Since that time, very extensive surveys have failed to find any more caves containing the species. In fact, Illinois cave amphipods have been found in only three of the six caves since 1986, despite repeated surveys in 1992, 1993, and 1995. The species is believed extirpated from two of the other three caves because it was last seen in them in 1965 and in 1986. In the sixth cave the current status of the amphipod population last documented there in 1965 cannot be determined because the private owner sealed the cave entrance. In 1999-2000, the amphipod was found in several other caves in two new watersheds, bringing the total number of extant populations to 10 in 6 drainage basins, all in Monroe County.

Threats: The contamination of the cave streams is believed to be the greatest threat to this species. The limestone bedrock in this area is pervaded by numerous caves which are connected to the surface by sinkholes and fissures. These surface openings provide direct and immediate connecting channels for surface pollutants to quickly reach the subsurface systems in high concentrations. Such surface pollutants come from the runoff of agricultural chemicals and livestock facilities, septic system leakage, improper disposal of chemical and other wastes, and intentional dumping into sinkholes. Especially high concentrations of such pollutants can be moved into the cave streams via the runoff from spring and summer rainstorms.

Water samples from Monroe County springs and wells have clearly documented widespread contamination by the agricultural pesticides atrazine and alachlor. Most sampled sites were also contaminated with high concentrations of bacteria species which likely originated from both human and livestock waste. The highest levels of atrazine that were found are close to the levels that are known to cause reduced reproduction and diminished survival of offspring in another amphipod species.

St. Clair and Monroe Counties are adjacent to the St. Louis metropolitan area. They are experiencing rapid residential development. Many of these homes utilize individual septic systems. Thus, deterioration of groundwater and subterranean stream water quality is expected to accelerate, making it less suitable for use by humans and aquatic organisms.

Two of the caves which still have the species are open to public use, via commercial tours in one, and by special permit in the second. These human incursions into the caves, including walking through the streams inhabited by the Illinois cave amphipod, may also be adversely impacting the fragile cave ecosystem; little research has been done on this issue. The third cave which currently has a population of the species has eight known entrances, all of which are privately owned. Human incursions into this cave are occurring; however, the use of the cave is at the discretion of the owners of the entrances and its extent is unknown.

Conservation and Research Recommendations:

  • Determine the surface recharge areas for the three caves known to have the species.

  • Reduce contamination of the recharge areas from agricultural chemicals, inadequate treatment and disposal of human and livestock sewage, and disposal of trash and debris into sinkholes.

  • Increase public appreciation of the need to protect the recharge areas of these caves, for both human and animal welfare.

  • Increase State protection for karst groundwater to improve water quality for cave organisms and human consumption.

  • Conduct additional surveys to locate new populations and to monitor the known extant populations. Periodically resurvey all historical populations to establish a trend.

  • Monitor water quality for pesticides, herbicides, PCB's, and bacterial contaminants in streams occupied by the Illinois cave amphipod.

  • Determine the short and long-term effects of the observed contaminants on related species of amphipods.

Protective Actions Underway:

The species is currently listed as an endangered species under the Illinois Endangered Species Protection Act, a designation that provides protection from direct killing or injury. It also requires State and local governments to solicit recommendations from the Illinois Department of Natural Resources prior to undertaking actions which may adversely impact the species. However, implementing those recommendations is optional.

Several of the entrances to caves containing the Illinois cave amphipod are dedicated Nature Preserves, the highest land protection instrument in the State.

Studies Currently Underway

  • Delineation of groundwater recharge areas for Illinois Caverns, Fogelpole Cave and Krueger Dry-run Cave

  • Surveys of caves in Monroe County to search for new populations of the species

  • Contaminant study of cave amphipod habitat

  • Develop non-lethal techniques for censusing the species

  • Monitor patterns of public use in Illinois Caverns

Studies Proposed

  • Delineation of groundwater recharge areas for Pautler Cave

  • Determine if public use has a detrimental effect on the species

Last updated: July 17, 2008