Spiders Forgoing Webs to Attack Prey Directly, Study Says

Many spider species have abandoned building webs to capture prey and instead attack directly, according to biologists at Kiel University and the University of Bern.

The spider's silken web, capable of ensnaring prey and protecting egg sacks, is partly responsible for the arachnid's ecological success. But the researchers have observed species of vagrant spiders making use of hairy adhesive pads called scapulae to hunt prey, often abandoning the web all together.

"More than half of all described spider species have abandoned building webs. They seize their prey directly and have to be able to hold and control the struggling prey without getting hurt themselves", said Jonas Wolff, a doctoral research student at Kiel University.  

The scapulae serve a similar function as the spider's sticky silk web; the hairs on the scapulae evolved as a substitute for silk in controlling prey. The finding upends previous research on why spiders evolved scapulae.  

Wolff said that earlier research tacked the spider's use of the hairy adhesive pads to climbing smooth surfaces and the hypothesis that the scapulae were used as a hunting tool received little attention. According to the research done by Wolff and his colleagues, however, locomotion was not the primary evolutionary purpose of the scapulae, but rather a secondary feature.

"Specialized foot pads, which enable the spider to climb steep smooth surfaces such as window panes, are further developments derived from the prey capture apparatus," Wolff said in a statement. "These results give us entirely new insights on the evolution of spiders." 

The research was published in the open-access journal PLoS ONE.