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Psyche 
[Vol. 87 
relationship between the areas occupied by spiders and the site of 
excreta deposition. These data indicated that spiders typically were 
associated with high-density silk sites (near the periphery of the 
containers) and, in contrast to the first model, that they deposit 
excreta outside their normal area of habitation. Thus, too many 
excreta were observed in areas of low silk density suggesting that 
sanitary behavior related to excreta deposition occurs in M. gregalis 
(Fig. 4). The limited amount of time spiders occupied the central area 
of low silk density (i.e. the outside of the web) suggest that, in part, 
they moved into this region in order to deposit excreta. Other 
possible reasons for visiting the central part of the containers include 
exploratory behavior and possible expansion of the web. Of the three 
models tested, the third is probably the most accurate as it depends on 
the actual distribution of living animals. As such, it indicates that 
animals deposit excreta at sites removed from their areas of 
occupation (i.e. in the area they treat as web-exterior). 
The malpighian tubules of spiders excrete guanine, adenine, 
hypoxanthine and uric acid into the cloaca with approximatly 
34-76% of the excretory material being guanine (Anderson, 1966). 
The relative insolubility of these compounds makes it unlikely that 
the smooth-surfaced excreta deposited on the floor of the chambers 
could provide potential growth sites for bacterial and fungal colonies. 
The excreta found on silk, however, were cracked and pitted. Such 
cracks could provide potential growth sites for colonies in a high- 
humidity environment; however, under the present conditions no 
such growth was observed. In a related series of experiments, colonies 
of various sizes (10-80 individuals) were housed in glass containers 
(13 cm dia, 17 cm height; Witt, personal communication). Initially, 
the majority of spiders inhabited only the upper portions of the 
vessels. After 4-6 weeks, however, they began to leave the main web 
and built a separate secondary web in the lower part of the container. 
Six colonies were available for my examination, all of which had 
contained spiders for over two months. Fouling of the lower Web by 
excreta was evident on examination of the colonies. In addition, both 
fly and spider carcasses exhibited evidence of fungal and / or bacterial 
growth. Dead spiders and prey in the upper portion of the containers 
typically did not support such growth. Evidently, animals located in 
the upper section of the containers dropped fecal material onto the 
lower web. These data suggest that, under certain conditions, 
bacterial and / or fungal growth is supported by fouling of the nest. In 
