SUBTERRANEAN ANIMAL LIFE 531 



and mites are almost entirely minute animals. Cave beetles are also 

 small, the species of Trechus, for example, measures 4 to 6 mm. Aquatic 

 forms become somewhat larger, though they too are small on the 

 average. Most cave fishes reach no more than 50 to 60 mm. in length; 

 only Amblyopsis spelaeus is larger and it may reach 135 mm. The olm 

 {Proteus anguineus) is a giant among cave forms, with a length of 250 

 to 285 mm. Occasional cave arthropods, however, grow to an unusual 

 size, larger than that of their relatives. Thus the giant amphipods in 

 the Balkan caves (Fig. 133) exceed 50 mm. in length; the springtails, 

 Aphorura gigantea and T etrodontophorus gigas, and the common cave 

 amphipod, Xiphargus, may reach a length of 30 mm. 



Some caves seem to be rich in food, to judge from the amount of 

 their animal life. The abundance of springtails in the Sosuvka Cave 

 has been mentioned. Vire took about 10,000 specimens of Niphargus 

 and 50,000 of Bithynella in one set of caves in southern France. The 

 snail Carychium is very abundant on wet wood in Mammoth Cave. 13 



Plant and detritus feeders serve as food for predaceous animals, 

 which are of course much less numerous. Spiders, pseudoscorpions, and 

 mites fill this role. Tiny mites, such as Pygmophorus, may be seen 

 carrying off springtails (Lepidocyrtus) ten times their size, and spiders 

 (Porrhoma) fifteen times as big as themselves. 14 A number of cave 

 snails in the Balkans are predaceous, as inferred from their radula. 12 

 Cave Orthoptera are also predaceous. The decapods (shrimps and 

 crayfish) are doubtless dependent on animal food. Cave vertebrates 

 are all carnivorous; the olm feeds on amphipods, Hydromantes on 

 insects. 



Lack of pigmentation. — The white or colorless character of many 

 cave animals must be attributed in some way to the darkness. Ex- 

 amples are to be seen in the cave planarians, the leech. Dina absoloni, 

 many crustaceans,* many springtails, cave snails, blind fish like Am- 

 blyopsis of the Mississippi region and Lucifuga of Cuba, and the olm. 

 Such colorlessness is not absolute, even among cave forms; the cave 

 fishes Typhlichthys and Troglichthys have traces of pattern, and most 

 cave spiders are more or less dark. Cave beetles are all pigmented, 

 though they may be paler than their relatives above ground. The 

 transitions in coloration may be seen in the fishes of the family Am- 

 blyopsidae. 15 Of the three species of Chologaster, C. cornutus lives in 

 surface waters in Florida, C. papilliferus lives in springs, under stones, 

 and C. agassizii is a cave fish, in the Mammoth Cave of Kentucky. 



* Niphargus and Asellus cavaticus, Palaemonetes antrorum, and Cambnnix 

 pell tic id II*. 



