1916 ENTOMOLOGICAL SOCIETY. 53 



In the grounds of the late Mr. Quartus Bliss, at Compton, in the eastern 

 townships, there was a horse-trough hewn out of a huge basswood log. The 

 water was supplied by a spring, and its overliow escaped at one end of the trough, 

 through a circular cut, and formed a puddle in the clay ground. One day, when 

 on a visit to Mr. Bliss, I saw a number of mud-wasps at this puddle gathering 

 soil, tempering it with their mandibles, and then flying away with pellets of 

 the cement. 



The cells brought to me were in masses, and probably numbered two hundred. 

 They reminded me of dirty peanuts jammed together. Within each was a long 

 oval chamber, at one end of which were the remains of the spiders on which the 

 inmate had fed. Next to these was a hard cap, rough and rounded on the out- 

 side, and concave and polished on the inside. Attached to this was a case, yield- 

 ing to the touch, and somewhat brittle, but strengthened by a fine silken covering, 

 which I found could be peeled off. 



The case was semi-transparent. The form of the waxen larva, free and 

 unattached, could be seen through it. Examined through a glass it appeared 

 to be formed of a like silken texture as its covering, but smoothed and compacted 

 by a vehicle that resembled glue or varnish. 



W 



y/ah si^e. 



Grub of Pelopceus cementarius (Drury) in the month of November. 



As the case was complete, and the remains of the spiders on the outside of 

 it, its occupant must have ceased to feed. 



The perfect Pelopceus is a grim object, very active, very forbidding. Its 

 " frightfulness " is its protection. It seems to say, " You let me alone, and I'll 

 let you alone." In reality it is one of our insect friends. 



I think three spiders for each would be a low estimate for the provision made 

 in the cells brought to me. That would give 600 spiders collected in the im- 

 mediate vicinity of the house in which the cells were found. Now, when you 

 call to mind how prolific the female spider is, you will be able to form a faint 

 idea of the terrible and disgusting plague from which the mud-wasps preserve us. 



But the spiders have their use in the economy of nature. Are there no 

 counter checks against the undue increase of the mud-wasps? Yes, several 

 ichneumon-flies have been recorded as preying upon them; for instance, Cri/ptus 

 junceus Cresson (Am. Ent, Vol. I, p. 137). 



Some years ago, I had a batch of Pelopfeus cells in my study window. One 

 day, when the wasps were breaking from their domiciles, I found a specimen of 

 Sarcophaga prcedator Zabriski in the window. I can only account for its presence 

 by supposing that it came from one of the mud cells. If my surmise is right, 

 how cnn wc account for the presence of intruders sucli as this in the mud castles 



