ENEMIES AND THEIK INFLUENCE. 389 



This genus is represented by a species, Argyrodes trigonum, 1 common in 



the neighborhood of Philadelphia and throughout the Eastern States. It 



makes the usual nest of crossed and netted lines common to its 



Argy- tribe, but is also parasitic in its nesting habits, for I have found 



it on the retitelarian section of the Labyrinth spider's web, 

 go num. 



where it had made itself very much at home. I have also found 

 it upon the webs of other species, as Linyphia communis and a small The- 

 ridium, and the upper intersecting supports and lines of Agalena nsevia. 

 Mr. Emerton 2 has observed the same tendency to nest parasitism, having 

 found Trigonum in the upper part of the web of Linyphia scripta and 

 also among the upper cross threads of Agalena nsevia. There is no record, 

 however, as far as I know, of this species actually preying upon its hosts, 

 and the creature must be endowed with unusual cunning if it really suc- 

 ceeds in doing so. 



The most decided example of this particular habit is found in a Line- 

 weaving spider described by Professor Hentz as Mimetus interfector. Hentz 



found the species in Alabama ; I have found it in Pennsylvania, 



Mimetus Ohio, New York, and elsewhere ; and Emerton has collected it in 



in^f^i*- 



f , Massachusetts and Connecticut. 3 According to Mr. Simon the 



species also occurs in southern Europe. 4 Hentz says that Inter- 

 fector spins a web resembling that of Theridium, but prefers prowling in 

 the dark and taking possession of the snares of Epeira and Theridium after 

 murdering the proprietor. 



This singular depredator is not rare, and was usually found by its dis- 

 coverer in houses, which enabled him to make many observations upon 

 its manners. The first specimen observed was a female, which had made 

 two cocoons under a table in his study, near and among the webs of sev- 

 eral individuals of Theridium tepidariorum. The cocoon of Mimetus is 

 oblong, and tapers equally at both ends, which are secured by many 

 threads connected with a retitelarian web. The mother was watching the 

 young, which were issuing from the lower one of her two cocoons. Thus 

 she appears to possess in a strong degree that maternal solicitude which 

 marks so many of her order. 



A second observation discovered a very different state of feeling as to 

 the young of other species, for she was observed devouring the eggs of 



Theridium tepidariorum, most probably after having eaten the 

 F ^ mother. A third specimen was found dead in the web of some 



species of Theridium, which no doubt had killed it, an illustra- 

 tion of the fact that sometimes in her predatory expeditions she man- 

 ages, like human robbers, to "catch a Tartar." A fourth Interfector was 



1 Argyrodes argyrodes Wick. 



2 Notes in Hentz's Spiders U. S., page 153. 



3 New England Spiders, Family Therididee, page 17. 



4 Arachnides de France, Vol. V., page 29. 



