816 



THE NATIONAL GEOGRAPHIC MAGAZINE 





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AS THE WASP LARVA GROWS, THE SPIDER SHRINKS 



After feeding for a \\'eck or ten da\'S, the larva is about one-ttrird grown 

 (upper). The spider is still alive, but will die quietly when its vital organs 

 are attacked. In the lower picture, the full-grown larva has devoured the 

 abdomen and is gnawing on a "drumstick," which she holds against her chest. 



drag the limp body back into tlie nest? 

 Possibly by studying the scenes of the kill- 

 ings I might find circumstantial evidence 

 that would answer these questions while I 

 was waiting for my cocoons to "hatch out.'' 



So T laid out a number of trapdoor tubes 

 containing cocoons, sat down at the table, 

 and proceeded as follows: 



Here is a group containing empty co- 

 coons. The lids are loose and work easily. 

 Obviously the "daughter" wasp, after 

 emerging from the cocoon, pushed up the 

 trapdoor and escaped that way. It is quite 

 possible that the mother wasp lifted the 



lid and entered the 

 tube to attack the 

 spider in the first 

 place, but there is no 

 evidence here to 

 prove that she did. 



Well, here is an- 

 other group, also con- 

 taining empty co- 

 coons, in which a large 

 hole has been gnawed 

 through each trap- 

 door, obviously by a 

 wasp, either to enter 

 or to leave the nest. 

 The lid itself is hard 

 to open, but that 

 might be because of 

 the mud washed into 

 the crevices by the 

 winter rains. There is 

 nothing here to prove 

 whether the mother 

 gnawed the hole to 

 enter or the daughter 

 to escape from the 

 tube. 



But there is still 

 another group of 

 nests, which contains 

 live wasp cocoons. 

 These trapdoors are 

 also gnawed through, 

 but they cannot be 

 raised. They are 

 sealed tight from be- 

 low with silk and 

 mud, which is the spi- 

 der's habit during the 

 hot summer months. 



At last, I've got the 

 goods on her! I know 

 that the young emerg- 

 ing wasp could not 

 have gnawed the hole in the trapdoor to get 

 out of the nest, because she is still inside, 

 sealed up in her cocoon. Therefore, her 

 mother must have gnawed the hole in order 

 to get in and attack the spider. 



So the circumstantial evidence proves not 

 only that Psammy enters the nest to attack 

 the spider, but it indicates that she recog- 

 nizes the trapdoor for what it is, seems to 

 know exactly what is hidden beneath it, 

 and goes right after her prey even if it 

 means tearing a hole through a sealed 

 trapdoor. 



So that was that. Afterwards I was able 







s 



