17MB PDF - Association for Mexican Cave Studies

182BIOLOGYSECTIONMEXICAN CAVE BEETLES OF THE FAMILY CARABIDAEby THOMAS C. BARR, JR •Institute of Speleology, University of Kentucky, LexingtonCarabids, or "ground beetles tl , are prevalent in many caves inall regions of the earth, but the cavernicolous species are but asmall fraction of the approximately 20,000 known species. Thesebeetles are for the most part predaceous, feeding on other smallinvertebrates, and are consequently beneficial or at least notharmful from an agricultural or medical standpoint. A few eatseeds and may be minor pests. The food is picked up in the mandibles,rotated by the palps, crushed or at least softened by therepeated working of the mandibles, and partially digested outsidethe body by enzymes poured out from the buccal cavity onto thefood. All available evidence indicates that cave carabids feedon other small cave animals, but they will certainly eat recentlykilled cave crickets, millipedes, or fragments of fish or beef.The cave carabids include troglobites (cave obligate species),troglophiles (species which can live either inside or outside ofcaves), threshold trogloxenes (species found in the tWilight zoneand dependent on food in the vicinity of the entrance, includingfood obtained outside the cave during night forages), and accidentals(species washed or straying into caves). The first 3groups are of greatest biological interest; the accidentals canusually be collected in greater abundance outside caves.TroglobitesTroglobitic carabids fall into two large groups, the tribesTrechini and Agonini, with a residuum of species belonging toother tribes which have few troglobitic representatives. Thetrechines are widely distributed throughout the world. With theexception of two or three tropical and subtropical genera, theyoccur in cool, moist, forested environments. The tribe is relativelywell known, thanks to the comprehensive, l80o-pageMonographie des Trechinae, by Dr. Ren~ Jeannel, published 1926­1930 in the entomological journal L'Abeille. Numerous genera andspecies of troglobitic trechines are found in the caves of southernEurope, from Spain to the Caucasus, in Japan, New Zealand, andin eastern United States. About 40 species of non-troglobitictrechines belonging to the genus Trechus occur in northern andmountainous regions of North America; T. aztec and T. tolucensisinhabit south-central Mexico but have not yet been ~aken fromcaves. Beetles of the genus Paratrechus constitute the principalelement of the Mexican trechine fauna; these occur in the mountainousregions and are rarely found in caves. However, in 1943Dr. Candido Bolivar y Pieltain described ~exatnae¥IPs prietoi fromLa Gruta del Palm1to, near Bustamante, N••, erst troglobitictrechine in North America to be discovered west of the MississippiRiver and the first known troglobitic beetle in Mexico (C1encia, 3:349-354). This beetle is elongate and slender, reddish-yellow