GENERAL CONSIDERATIONS. 91 



animals is very marked. This influence is very noticeable with the 

 flies and spiders, and to some extent with the myriapods, thysanurans, 

 and beetles. 



There seems in most cases a direct relation between the temperature 

 and the activity of those insects which hibernate near the mouth of the 

 cave. These hibernating insects become more active when subjected 

 to a rise in temperature even in the midst of winter, while if subject to 

 a temperature of 5° C. or lower they are barely able to stir. These 

 remarks apply to these insects when disturbed. They apparently move 

 very little or not at all otherwise. 



Many species in the portion of the cave near the mouth retire into 

 cracks and small holes or short side-passages, so that the abundance of 

 life is apparently greatly diminished in the winter. Phanetta subterranea 

 and the other spiders which live under rocks and debris become quite 

 inactive; Theridium kentiickyense, Tegenaria derhami, and other spiders 

 which have webs on the wall crawl into cracks; the myriapods apparently 

 do likewise or conceal themselves under debris; and the helomyzid flies 

 and Ldmosina tenebrarum withdraw into cracks and crannies of the wall. 

 The latter also conceals itself under debris. This marked change in 

 the cave life is not so noticeable beyond "17." Animals which are not 

 near enough the mouth to be subjected to great changes in temperature 

 show a variation in their activity in proportion to the change to which 

 they are exposed. Beyond the mound the fluctuation in temperature is 

 so small, however, that it produces no noticeable influence upon the 

 activity of animals in the cave. Here the true cave forms of whatever 

 order are equally active at all seasons. 



As far as observed cave animals do not breed during the winter in 

 those parts of the cave where the temperature becomes lower than about 

 9° C. With the coming of the higher temperature again, the spring 

 freshets having meanwhile left an abundance of organic matter in parts 

 of the cave, many cave species begin to breed abundantly. This activity 

 is very marked in the flies, especially the species of Leria, Oecothea fenes- 

 tralis, and Ldmosina tenebrarum, the spiders, the myriapod Conotyla 

 bollmani, and the beetles Rheochara lucifuga and Quediits spelsms. The 

 Diptera mentioned become extremely abundant and by about June 10 

 have reached their maximum in number. All species in those parts of 

 the cave appear to become more abundant in spring. This increase is 

 probably a real one due to the animals breeding freely, and an apparent 

 increase due to the greater activity of the individuals and their having 

 come out from the obscure places in which many of them spend the 

 winter. It seems possible that many Helomyzidae and perhaps other 

 Diptera are reared outside the cave and enter it early in the summer. 



