18 WHEELER— THE PARASITIC ACULEATA. 



insects. That the Poinpilus suspects the hostile intentions of the Ceropales 

 is clear from the behavior of a P. viaticus that hid with her spider among 

 the dense grass-blades of a road-side and would not venture into the open 

 because she was being watched by two female Ceropales each perched on a 

 grass-blade, stretching its antennse downward and edging nearer from time 

 to time. The angry Pompilus finally gave chase to the parasites and only 

 after they had flown away did she leave her concealment with her prey. 



"When a spider on which a Ceropales has just alighted is examined, 

 the egg cannot be seen at first because it is placed in such an unsuspected 

 spot. At the base of the ventral surface of the abdomen the spider has two 

 slit-shaped stigmata which open into the lung-books. The wasp inserts her 

 egg into one of these. The stigmata look like pockets, with very closely fit- 

 ting flaps. After the egg is in place the orifice of the pocket sometimes 

 gapes slightly so that one end of the egg can be seen. This is apt to be the 

 case in Drassodes, but in the large Lycosids the pockets are so capacious 

 that they completely conceal the egg. The place is obviously selected be- 

 cause in it the egg is perfectly protected when the spider is later dragged 

 into the burrow by its rightful owner, for it is evident that if the egg were 

 merely attached to the surface, it would be exposed to serious injury while 

 the spider is being drawn through the narrow burrow. The last abdominal 

 segment of the female Ceropales, which is constructed like a short, flat, 

 truncated ovipositor — a structure vmique among the solitary wasps — evidently 

 represents an adaptation to the narrow, slit-shaped stigmata, since the latter 

 can be opened by means of such an instrument and the egg inserted. Not 

 infrequently I have seen an egg in each of the lung-books of the same spider. 

 Since the Pompilus later attaches its own tgg to the side of the spider's 

 abdomen, the situation becomes very complicated, as there are then three 

 rival claimants for the same spider which is sufficient food for only one. A 

 few successful breeding experiments have revealed the drama that is subse- 

 quently enacted in the dark burrow. 



" After an embrj'onic period of two to three days, the Ceropales larva 

 hatches. Its anterior portion, as far back as the tenth segment, extends 

 straight out from the stigma, while its posterior portion remains concealed 

 in the lung-book. Soon the exposed portion is seen to bend downward till 

 the head touches the spider's belly and the larva begins to feed. As soon as 

 the Ceropales in the other lung-book hatches the older larva evidently smells 

 a rival, for it stops feeding, stretches itself out and moves its anterior end 

 freely about in the air in the direction of its competitor. The latter is at 

 first out of reach, but as soon as the older larva has fed and grown suffi- 

 ciently in length it attacks its younger companion, which is quite unable to 

 escape its fate. After its cannibal feast the Ceropales larva again bends 

 down and continues to devour the spider. Not till several days have elapsed 

 does the Pompilus larva hatch, although the egg was laid not more than a 

 few hours after the Ceropales egg. When the Pompilus larva begins to 

 grow the Ceropales larva becomes aware of a new rival and turns in its 

 direction. When a little later it has grown sufficiently to reach the Pompilus 

 larva, the latter's fate, too, is scaled. With the elimination of its last com- 



