Spider size is a surprisingly interesting topic, with quite quick evolutionary changes in both directions, and lots of interactions between spider size, web siz

Spider size is a surprisingly interesting topic, with quite quick evolutionary changes in both directions, and lots of interactions between spider size, web size, prey size, etc. Here's an excerpt from a book about some effects that influence the size of orb-weaver spiders (internal citations omitted): Spider size has evolved rapidly and diversely throughout the evolutionary history of spiders, both in terms of absolute size and relative sexual size dimorphism. In general, there seems to be a trend towards increased spider body size, especially for females, across the phylogenetic tree. ... For orb web spiders, the most common explanation is likely fecundity-based female gigantism because clutch size, the most commonly used proxy for spider fecundity, generally strongly correlates with female body size both intra- and inter-specifically. ... [M]ight the function of orb webs also play a role in spider size evolution? We believe the answer is yes. In general, orb web architecture determines the type of prey intercepted and retained that could be consumed by the spider. Thus, spider size evolution may occur under selection for how webs might fill 'empty niches'. For example, tiny anapid and mysmenids build orb webs that capture insects ignored by larger orb-weavers, and theridiosomatids specialize on mosquitoes that are too small to be relevant to the diets of large spiders but also such specialized fliers that they are rarely captured by the webs of other, less-specialized spiders. ... Similarly, the largest orb-weavers make webs powerful enough to retain the largest insects, which are simply not available to smaller spiders, and their webs can sometimes even subdue vertebrate prey. Orb webs may place an upper limit on the maximum size achievable by orb web spiders due to increases in the costs of producing webs in larger spiders and due to differences in how the kinetic energy of insect prey versus the stopping powers of orb webs scale with size. Source: http://www.amazon.com/gp/product/0124159192/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=0124159192&linkCode=as2&tag=kmjn-20 http://www.amazon.com/gp/product/0124159192/ref=as_li_ss_tl?..., pp. 225-226