138 AMERICAN SPIDERS 



distinct septum, on each side of which lies a spinning field. Because 

 of this division, the hackled band spun by Amaurobius consists of 

 two ribbons instead of the one band usually found in the cribellates 

 that have obliterated the limits between the two spinnerets. The 

 two ribbons are borne by two strands of dry silk presumed to come 

 from the ampullate glands. To spin its composite hackled band, 

 Amaurobius holds the hind leg of one side at right angles to the long 

 axis of its body, with the tarsus resting against the metatarsus of the 

 leg of the other side. The metatarsal comb is then rubbed back and 

 forth over the cribellum, drawing out two ribbons that are attached 

 to two lines of dry silk coming at the same time from the spin- 

 nerets. After a period of incessant spinning, the spider shifts to the 

 other leg, supporting it as before by resting the tip across the oppos- 

 ing metatarsus. The result is a fairly regular, ribboned band of silk 

 that seems to the naked eye a single thread, and has a characteristic 

 bluish color. 



The cribellate spiders have retained more units of spinning 

 equipment than have any other true spiders, and have maintained 

 all of them as functional organs. It is thus not surprising that none 

 have become truly vagrant, and that all rely to a very large extent 

 on their viscid threads to capture insects. The very fact that they 

 have retained the cribellum, with its glands of sticky silk, indicates 

 their reliance on it in some measure to entangle their prey. 



In the cribellates, the unpaired claw on the tarsus is usually pres- 

 ent, but it is lacking or reduced in size in a few members that may 

 be taking their first steps toward becoming vagrant types, or have 

 learned to do without these tarsal hooks in their webs. Some cribel- 

 lates are confirmed aerial spiders and spin tangled webs, sheet webs, 

 and orb webs, from which they hang downward. Others run over 

 an irregular blanket of webbing in an upright position. The cribel- 

 late spiders have produced web structures closely paralleling those 

 of the ecribellate spiders, the only difference being the use of the 

 hackled band by the former. 



The cribellates are quite sociable creatures. During the mating 

 season the males enter the webs of the females and live there as 

 partners until presumably they die a natural death. This tolerance 

 carries even beyond the mating season, for among the cribellate 

 spiders we find nearly all our social spiders. Some members of al- 

 most every family are known to live together, in colonies similar to 

 those of certain gregarious caterpillars. 



One of the controversial and perplexing problems in spider 



