THE AERIAL WEB SPINNERS 175 



spines between, forming a rake on the metatarsi and tarsi of the 

 front pairs of legs. Other structural details would seem to ally the 

 pirates either with the sheet-weaving linyphiids or the orb weavers, 

 but their virtual failure to use silk in any way keeps their position 

 obscure. In many respects they resemble the enigmatic Archaeidae 

 from Baltic amber deposits, modern species of which have been dis- 

 covered in South Africa, Australia, New Zealand, and southern 

 South America. 



About a dozen mimetids occur in the United States. Typical 

 situations are ground debris, vegetation, and, of course, the webs of 

 other spiders. The species of Mimetus are about one fourth of an 

 inch long, and have rounded abdomens with two angled humps 

 above the base. The species of Ero are about half as large, shaped 

 much like Mimetus, and have small humps on the top of the ab- 

 domen, with a covering of stiff brown hairs. The egg sacs of Ero 

 are spherical bags covered with a loose network of brownish silk; 

 this is twisted to form a thread by which the bag is suspended above 

 the ground. 



All the mimetids are slow-moving, stealthy cannibals that have 

 become experts in their nefarious trade. Mimetus preys on the orb 

 weavers and the comb-footed spiders, and in the South is frequently 

 found in the webs of Tidarren fordum. Ero attacks and subdues its 

 prey with an expertness that belies the animal's seeming innocence. 

 This small pirate will craftily enter the tangled lines of TheruKotfs 

 web, and clear a space of threads without making its presence 

 known to the occupant. When all is prepared, Ero pulls at the 

 lines, then awaits the approach of the aroused spinner, which hur- 

 ries to the spot with customary confidence. At just the right mo- 

 ment, Ero grasps the legs and body of Theridion with its long front 

 legs, and, holding on firmly with the coarse rake of spines, quickly 

 bites the femur of the victim's front leg. A complete collapse of 

 Theridion, the consequence of a remarkably virulent venom, is al- 

 most instantaneous, and the victor immediately begins sucking the 

 body juices from the bulky prey. Only on rare occasions are the 

 tables turned, and the pirate made a victim of its own seduction. 



THE ORB WEAVERS 



The two-dimensional snare known as the orb web is a crowning 

 achievement of the aerial spiders. To the layman the web is an 



