THE MUD-DAUBERS. 193 



use large spiders and should always liave them fresh, but it is 

 evident that tastes differ and the matter is so purely a subjective 

 affair that it will have to go unsettled. In any event whether 

 her victims be strong or feeble, old or young, big or little, fresh 

 or dry, they certainly serve admirably in enabling Pelopaeus 

 to rear brood after brood and to people the different parts of 

 the earth with abundant representatives of her kind. 



If any conclusion can be drawn from our observations 

 it is that there is no importance to be attached to the number of 

 spiders stored, to whether they are large or small, to the plac- 

 ing of the egg on the first or on the last victim, nor even to the 

 state of the spiders, since those that are killed at once by the 

 stroke of the beautiful assassin serve their purpose just as well 

 as those that are paralyzed, and lie collapsed and powerless, all 

 unconscious of their approaching fate. 



At the close of the period of alimentation the larva spins its 

 cocoon, which, light-colored at first, turns darker in the course 

 of a few days. Here it remains, perhaps for a few weeks, or 

 perhaps until the following spring. When it is ready to emerge 

 there exudes from its mouth a quantity of watery fluid which 

 serves to soften the cover of the cell so that it may easily gnaw 

 its way out. While watching a number of young wasps both 

 of the yellow and the blue species just as they were leaving the 

 nest, and even before their wings were ready for flight, we 

 noticed that when touched they at once attempted to sting. 

 This would seem to prove that the stinging habit is congenital 

 and instinctive. 



We have made a number of experiments on different inverte- 

 brate animals to determine the effect of the venom of the wasps 

 w^hen injected into different parts of the body. Our first effort 

 was to discover whether animals could be killed by allowing 

 them to be stung several times at a point remote from the cen- 

 tral nervous system. For this, we took a small crayfish, two 

 and one-half inches long, and removed the first ambulatory 

 leg at the basal joint, and then held an individual of Polistef^ 



fusca in such a way that it thrust its sting into the exposed 

 13 



