1977] 
Robinson — Insects and Spiders 
231 
The evolution of finely adjusted interspecific relationships must 
have involved innumerable adaptive steps that are almost incon- 
ceivable in their probable complexity. Lepidopteran larvae (and 
other spiders) may be, as producers and manipulators of silk, some- 
what preadapted to evolve symbioses with web-building spiders. 
Adult butterflies and moths are probably less endangered by sticky 
spider silk than are most other insects (Eisner, Ettershank and 
Alsop, 1964) and this could reduce some of the dangers involved 
in evolving symbioses with spiders. Nonetheless, the caterpillars 
had to solve two major problems. They had to in some way sup- 
press the predatory responses of the spiders to objects moving on 
the web and also develop a system of detecting their own food 
within the web. From my own observations I would conclude that 
both Stegodyphus sp. and Anelosimus eximius are much less re- 
sponsive to gently moving objects in their webs than are many 
orb-weavers. It may have thus been slightly less dangerous for 
moving caterpillars to invade these webs in the first place, but I 
strongly suspect that the present immunity to spider attacks de- 
pends on something more than the caterpillars “walking softly.” 
Acknowledgments 
I am extremely grateful to Dr. E. L. Todd, Systematic Ento- 
mology Laboratory, IIBII Institute, U.S. Department of Agricul- 
ture, for identifying the moths. My thanks to Dr. F. Vollrath of 
STRI for access to unpublished observations and for helpful com- 
ments. 
References 
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Bristowe, W. S. 
1941. The Comity of Spiders. Vol. II. Roy. Soc. London. 
Eisner, T., R. Alsop and Ettershank, G. 
1964. Adhesiveness of spider silk. Science 146: 1058-1061. 
Levi, H. W. 
1955. The spider genera Neottiura and Anelosimus in America (Araneae: 
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