Field Studies of the Non-Social Wasps 457 
the cell was again empty. She then remained on the 
nest holding watch for thirty minutes, as if resolutely 
waiting to catch the hoodoo. When she left, I expected 
her to refill the nest with spiders of her own capture, 
but instead she brought a load of mud and, to my amaze- 
ment, spread it in a thin layer on the inside of the cell, 
as though the very walls were polluted, or else all of 
the trouble were due to its inadequacy. So, for the first 
time, I saw a wasp adding mud to the inside walls of a 
cell after she had once deemed it finished. . 
The next day at 3 p. m. she was still coming to the 
cell occasionally with an air of angry suspicion and un- 
certainty, but otherwise it was in the same empty con- 
dition that I had left it. Unfortunately, I was obliged 
to leave on the evening train, so I never knew what she 
finally decided to do. 
Exp. XII. At six o’clock one August evening I filled 
& new one-celled Sceliphron nest with spiders from an- 
other nest during the absence of its owner. I was called 
away and could not observe it further until the next 
day, when I found the cell sealed. I opened it and found 
that my substitutes were gone and in their stead were 
two other spiders. The mother had evidently begun to 
fill the cell after having thrown out my spiders, but had 
stopped with only two and sealed the cell without hav- 
ing even deposited her egg. 
Exp. XIII. A certain nest of a mud-dauber was 
almost complete when I filled it with spiders from an- 
other nest. The proprietress returned with a load of 
mud to add another ring. When she saw the spiders she 
withdrew her head with a start, as though greatly 
shocked. Again she inquiringly put in her head, with 
like result. She then went away in bewilderment and 
returned six times, but each time sought the nest at a 
