114 
Psyche 
[Vol. 92 
occur in web building behavior is not clear. Simple adaptive explana- 
tions of the changes in spiders’ behavior seem unlikely in at least 
some cases: for example an open sector allowing easier access to the 
web from a hidden retreat would seem advantageous for young as 
well as older individuals of Zygiella; and the displacement of the 
hub toward the top of Nephila webs would presumably result in 
more rapid attacks by young as well as older spiders (Masters and 
Moffat 1983). Some arguments attempt to explain the relative con- 
servatism of younger individuals’ morphology as a result of the 
young being shielded from the action of natural selection from the 
surrounding environment (e.g. Darwin 1859), and are clearly not 
applicable to the webs. Others cite the effects of canalization in 
development and the likelihood that modifications expressed earlier 
in ontogeny will have especially low adaptive values because their 
consequences are magnified by subsequent growth (see Futuyma 
1979, Gould 1977). This is probably true for some morphological 
traits, but innate behavioral characters do not obviously build upon 
each other, and the argument thus loses credibility. Young spider- 
lings are able to spin complete orbs the first time they try, and in at 
least some cases (e.g. Eustala sp., Fecenia, Scoloderus) the spider- 
lings’ webs are made of (presumably) similar types of silk used in 
approximately the same relative quantities as the silk in adult webs. 
Learning probably plays little part in the ontogenetic changes in 
orb-weavers’ behavior (Petrusewiczowa 1938, Mayer 1953, Reed et 
al. 1970, Robinson and Robinson 1976). Thus the reason for greater 
conservatism in juvenile web design remains a mystery. 
Acknowledgements 
The observations were made while I participated in an O. T. S. 
field course led by D. Futuyma and F. Putz. H. W. Levi kindly 
identified spiders, and he and M. J. West-Eberhard read a prelimi- 
nary draft of the manuscript. Discussions with D. B. Wake helped 
focus questions regarding ontogeny, and Y. D. Lubin, A. Deccae 
and R. Jackson generously allowed me to use unpublished observa- 
tions. Financial support was provided by the Vicerrectoria de Inves- 
tigacion of the Universidad de Costa Rica. 
