More Than Half of Spiders No Longer Build Webs
Spider webs are beautiful to behold, but they're not necessarily all that efficient to use. For spiders that weave webs to hunt, their foraging is effectively restricted to one area. Moreover, ignorant and unappreciative humans frequently rip the elegant, silken constructs to shreds, leaving the eight-legged owners temporarily without means to attain nourishment.
Perhaps due to these stark limitations, more than half of spider species have abandoned the web-spinning ways of many of their forebears, instead pursuing prey in a more traditional "search and seize" manner.
Using hairy adhesive pads called scopulae, affixed to their anterior legs, these free-hunting spiders track down and seize their prey. The scopulae come equipped with thousands of sticky, microscopic hairs called setae. When erect, the hairs mercilessly cling to whatever they come in contact with. All the benefits of a gluey web are available to go.
Conducting a phylogenetic analysis across tens of thousands of spider species, researchers at the University of Kiel in Germany found that almost 83% of free-hunting spiders feature these setae, while only 1% of web-building spiders do. Clearly, the tiny hairs are a key differentiator.
"This indicates that [setae] are adaptations to a free hunting lifestyle," the authors say.
We may indeed be witnessing a noticeable example of evolution in action. Over the coming centuries, it will be quite interesting to see if more and more spiders switch to a web-less hunting style. If so, pristine, silken webs sparkling with dew on a clear, spring morning may, sadly, become a rare sight.
Source: Wolff JO, Nentwig W, Gorb SN (2013) The Great Silk Alternative: Multiple Co-Evolution of Web Loss and Sticky Hairs in Spiders. PLoS ONE 8(5): e62682. doi:10.1371/journal.pone.0062682