i 7 4 AMERICAN SPIDERS 



that the head modifications, even though pits are absent, may be 

 associated with interesting copulatory routines. The conclusion 

 that modified heads and pits have arisen quite recently and inde- 

 pendently in various groups of erigonids is supported by the close 

 relationship with species that do not exhibit these secondary sexual 

 characters. 



Among the most interesting spiders of this subfamily are some 

 that have become typical cave forms. Anthrobia mawmouthia, 

 found in the Mammoth and other caves in Kentucky, has lost all 

 traces of eyes. It lives under stones in the cave, there spinning small, 

 flattened egg sacs that contain a few unusually large eggs. Another 

 tiny species, Phanetta subterranea, is a characteristic feature of cave 

 systems from Indiana and Kentucky to Virginia. All its eyes are 

 usually present, but frequently they are much reduced in size, and 

 occasionally the anterior median pair is missing. 



The cave spiders of the subfamily Nesticinae resemble the 

 theridiids in appearance, and have a somewhat similar comb of 

 toothed bristles on the hind tarsi, but their mouth parts and genital 

 organs ally them with the series of sheet web spinners. Their webs 

 are loosely meshed sheets and tangles hung on the walls of caves or 

 hidden under stones. The females drag globose egg sacs around 

 with them, attached to the spinnerets in wolf-spider fashion. The 

 nesticids always live in dark situations, evidencing a decided predi- 

 lection for caves, mines, and tunnels. They are pale spiders; their 

 eyes are reduced in size or missing; and their allegiance to cave life 

 is reflected in their loss of pigment. 



Several different nesticid types occur in the United States. A 

 darkly marked species, Nesticus cellulanus (introduced from Eu- 

 rope), lives in cellars and in dark corners in houses and barns. Our 

 common Nesticus pallidus, a pale yellow spider, one seventh of an 

 inch long, found all over North America, lives under stones or 

 boards on the ground, in burrows and cave entrances, and deep in 

 totally dark caverns. Outdoors specimens all have normal, well- 

 pigmented eyes, whereas some cave dwellers have lost the anterior 

 median pair. 



The pirate spiders (family Mimetidae) are curious aerial types 

 that creep into the webs of other spiders and kill them. These hand- 

 some cannibals, so far as is known, feed exclusively upon other 

 spiders and never use silk for a snare. Their bodies are delicately 

 marked with dark lines and spots. A principal feature is the pres- 

 ence of a series of very long, regularly spaced spines, with smaller 



