16 CYRTIDAE OF NORTH AMERICA 



the wing. These eggs were black, papillose and pear-shaped, and 

 did not hatch until forty-nine days later. This female laid 

 eight hundred and nine eggs, another nine hundred and five. 

 One lot of eggs laid April 12 hatched June 2. I placed some of 

 the minute larvae on spiders {Theridium tepidariorum Koch) 

 and they at once attached themselves to the legs and body of the 

 host. The spiders scratched frantically at first and were seen to 

 kill some of the larvae with their jaws. The larvae when attached 

 would usually stand out straight from the body of the spider, re- 

 sembling erect bristles. They were gray in color, twelve-seg- 

 mented, including the head, and with whitish bands between the 

 segments and black bristly hairs. When not attached they were 

 very active. They were able to follow along a single thread of a 

 spider web, usually proceeding like a looper. Only one mature 

 larva was found in a spider web and this one died as it was pupat- 

 ing. The work on Opsehius was interrupted before any mature 

 larvae covild be reared and all of the material was lost. 



I have found nothing in literature in regard to the behavior of 

 spiders when confronted with one of these Cyrtid parasites and it 

 is interesting to note their actions. I placed an adult female of 

 Opsehius diligens in a battery jar, with a large female spider which 

 had filled the bottom of the jar, with its web and was standing 

 guard over its egg case. The fly paid no attention to the spider 

 and kept on floundering through the web, scattering eggs as it wejit. 

 The spider appeared quite disturbed and would run up to it and 

 then turn and run back to the egg case. On one occasion the fly 

 approached very near this treasure and I prepared to rescue it 

 when the spider came rushing out, but no interruption was neces- 

 sary. The spider tried to scare away the little intruder Ijy nip- 

 ping at it but soon lost courage and ran back in her tunnel. This 

 is all the more remarkable in view of the fact that the spider had 

 not been fed for two or three days. To test her I threw in a 

 couple of house flies and saw them crushed and carried into her 

 parlor without any hesitation; a large blue bottle fly met the same 

 fate. There seems to be some recognition on the part of the 

 spider that this small fly is something out of the or '"^''ary. It 

 may have an instinctive dread of its parasite and rcce i;nize it at 

 once. The continTial hunnning noise made by this fl. .is not 

 the cause of this fear, for the body of a freshly killed specimen was 



