Prey Selection in an Orb-Weaving Spider: Micrathena Gracilis (Araneae: Araneidae)

A number of studies have examined the prey captured by web building spiders, and many have compared the captured prey with the insects available in the environment (Bilsing 1920; Turnbull 1960, 1962; Cherrett 1964; Kajak 1965; Olive 1980; Nentwig 1980, 1983; Brown 1981; Shelly 1983, 1984; Robinson & Robinson 1970, 1973; Riechert & Tracy 1975; Uetz et al. 1978; Chacon & Eberhard 1980; Uetz & Biere 1980; Riechert & Cady 1984). The most common comparisons are between prey found in webs and the "potential prey" captured by traps that in some way mimic spider webs (sticky traps, windowpane traps, etc.). Although there is disagreement about What kind of trapping method most accurately assesses the prey actually available to spiders (see Uetz & Biere 1980; Chacon& Eberhard 1980; Shelly 1984), all these studies suggest, to a greater or lesser extent, that the range of prey taken by spiders demonstrates some degree of selectivity. Recent research has shown that specialization is the result ofweb placement, web structure, and behavioral choices in the attack process (Chacon & Eberhard 1977; Uetz & Biere 1980; Riechert & Luczak 1982; Nentwig 1983; Shelly 1983, 1984; Riechert & Cady 1984; Craig 1986; Stowe 1986). An important question that many of these studies have addressed concerns the role of the spiders’ web in the selection of prey, and why some prey insects are trapped more or less efficiently than others. Most workers agree that the process by which insects fall prey to spiders in their webs is neither random nor passive because insects vary in their ability to avoid webs, or escape from them once caught (see Nentwig 1982; Craig 1986); and web design and function favor capture of specific prey types and sizes (see Riechert & Luczak 1982; Rypstra 1982; Stowe 1986). The capture of insects by spiders on the