96 ZOOLOGY 



hide during the day, it is easy to understand that the cave 

 affords a favorable environment for such a Ught-shunning 

 species. 



The springtails, some of which hvc in caves, are among the 

 smallest and simplest of insects, and perhaps the most numer- 

 ous ui individuals (Fig. 97). On a single bare beach one-fourth 

 of a mile long the number of springtails hving 

 between high and low tide has been estimated 

 at 100,000,000. The group as a whole love.s 

 moisture. They also love contact, so one sees 

 them burrowing into the sand. They are 

 seen to be most numerous at night ; they 

 shun the light. Finallj', they feed on any 

 organic debris. This is e\'identh' a group 

 that is fitted to live in caves, and so the 

 siiringtails are found in the caves of both 

 Fig. 97.-- a spring- America and Europe. Some of them in the 



tail. (FroinParkrT ^.j^^.gg ^^^ |-,li„(l ^nd ColorlcSS. But tllis COn- 

 aad H a y w e U ' s 



Text -book of dition is not to be attributed only to the 

 Zoology.) absence of light, for some of the allies of the 



cave springtails that live above ground are colorless and l)lind. 

 Also some of the indi\'iduals of one species, at least, live ahove 

 ground, while other indi%'iduals hve in caves. Both sets shun 

 the light of daj' ; but it is onlj' certain fortunate individuals 

 that have got into caves. 



Most of the spiders that live in caves are related to those 

 that build cobwebs in our cellars and Ijarns. It is easy for 

 such lovers of darkness and moisture to find a suitable home 

 in caves. But the cave sjiecies live under stones and make 

 only a few strands of web. They seem to feed on the larger 

 springtails. 



