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When cave crickets go out for dinner, they really go, researchers say

September 08, 2005

CHAMPAIGN, Ill. - Cave crickets travel farther from their homes to forage - by about double - than their previously reported range, researchers have discovered. In Texas, that means protective buffer areas around caves may need to be extended to protect endangered invertebrate species that live inside and depend on the crickets.

Reporting in the journal American Midland Naturalist, a team of researchers led by Steven J. Taylor, an entomologist with the Illinois Natural History Survey and University of Illinois at Urbana-Champaign, reported that the crickets, Ceuthophilus secretus, journey at night in high numbers up to 80 meters (262 feet) from the entrances of central Texas caves. A few crickets traveled up to 105 meters (344 feet) to feed.

Previous research indicated that most crickets stay within 50 meters (164 feet) from their caves. As part of the formula for a buffer zone proposed by the U.S. Fish and Wildlife Service, a range for cricket foraging was recommended. The buffer zone also extends outward to control for the effects of invasive red imported fire ants (Solenopsis invicta Buren). The buffer-zone formula helps to guide where to apply treatment applications against the ants.

Buffer zones are designed to help maintain a healthy vegetative community, including woodland and grassland species, around cave entrances to protect cave life from disturbance, including that created by encroaching urban development.

"Our findings suggest that a relatively large area may be needed to protect the crickets' foraging area and to shield them from fire ants," Taylor said. "Based on the foraging range we saw, we believe that cave resource managers may wish to create buffers around the footprint of a cave - not just the entrance. It could be that there are other small openings that allow crickets to leave caves on their way to forage."

The U.S. Fish and Wildlife Service has listed 16 cave invertebrates - including a variety of spiders, pseudoscorpions and beetles - in the Austin-San Antonio region as federally endangered species. These invertebrates depend on nutrients brought into caves primarily by crickets after foraging. Crickets also lay their eggs inside.

Taylor and colleagues studied the crickets around a cave at Fort Hood, a sprawling military base northwest of Austin. Both cave crickets and fire ants are found in large numbers around the cave, in which several invertebrates related to endangered species live.

Researchers collected crickets as they emerged from the cave during late spring and summer in 2003. Using a fine-tipped brush, scientists, in the course of 17 nights, marked more than 2,000 crickets with fluorescent water-based paint. The crickets were then released each night within a meter of the cave entrance. Later each night, the crickets were located using portable black lights, with their locations plotted with GPS equipment. On subsequent days, the locations were measured and analyzed.

On average, adult crickets were found farther from the cave entrance than were the nymphs. While 51 percent of all crickets were found to be within 40 meters (131 feet) of the cave entrance, 8 percent were found at locations 80 meters (262 feet) and beyond.

Previous studies of cave-cricket foraging depended on the use of bait stations, which, Taylor said, could have biased the distribution and movements of the crickets by attracting them to energy-rich locations. The use of paint on the crickets, he said, made it "more likely that observed foraging distances are natural."

"Our results provide a quantitative measure of cave cricket foraging range," the researchers wrote, "and indicate that Ceuthophius secretus routinely forages out to 80 meters or more from the cave entrance, and is relatively uniform in density out to this distance."

Co-authors on the study were Jean K. Krejca of Zara Environmental LCC in Buda, Texas, and Michael L. Denight of the Engineer Research and Development Center at the Construction Engineering Research Laboratory in Champaign, Ill.

University of Illinois at Urbana-Champaign