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Psyche 
[Vol. 94 
which suggests that it should be more efficient in attacking fast- 
escaping but relatively harmless prey. Prey size is probably a more 
important criterion in prey selectivity for such a species than is prey 
type. The hunger level of the spider may also play an important role in 
what the spider may choose to attack, but it is a difficult parameter to 
control in observational field studies such as this. Spiders are often 
subjected to severe food shortages (Olive 1982) and may switch from 
being a specialist to a generalist, i.e. accept a less preferred prey item 
due to the paucity of preferred prey types (Emlen 1966; Schoener 
1969, 1971; Pulliam 1974; Lacher et al. 1982). 
The degree of selectivity shown by Micrathena gracilis is surely not 
as precise as many prey specialists (see Stowe 1986). However, given 
that any specialization should be risky for a spider with its attributes, 
this prey selectivity must pay off in providing this species with an 
apparently adequate diet. 
Summary 
The prey of a common deciduous forest orb-weaver, Micrathena 
gracilis (Walckenaer), was compared with potential prey sampled by 
artificial sticky web traps. Comparison of traps and webs indicated 
that webs of Micrathena are selective, showing selectivity for Diptera 
sized greater than 3 mm, even though the majority of prey hitting 
webs and in traps are much smaller. Spiders also showed selectivity in 
attacking larger dipteran prey, and ignoring the majority of tiny 
insects (< 3 mm) stuck in their webs. Prey specialization seen in 
Micrathena appears based primarily on insect size, and is likely 
related to the profitability (energetic reward) of larger Diptera as 
prey. 
Acknowledgements 
This research represents a portion of a thesis submitted in partial 
fulfillment of the requirements for the degree of Master of Science in 
Biological Sciences at the University of Cincinnati. 
We thank the Cincinnati Park Board for use of their parks. We are 
grateful to G. Stratton, C. Meininger, T. Bultman, W. Hopple, J. 
Fisher, D. Francis, N. Folino, P. Bianconi, and J. Stout for diverse 
assistance in field and lab. We also appreciate the help of T. C. Kane, 
A. Butz, and M. Hodge for reviewing earlier drafts of this manus- 
cript. Thanks also to M. Killeen for typing. 
