Economics of spider orb-webs: the benefits of producing adhesive capture thread and of recycling silk

1. The replacement of dry, fuzzy cribellar prey capture thread by viscous, adhesive capture thread was a major event in the evolution of orb-weaving spiders. Over 95% of all orb-weaving species now produce adhesive threads.
2. Adhesive thread achieves its stickiness with a much greater material economy than does cribellar thread.
3. Transformational analyses show that, relative to spider mass, adhesive orb-weavers invest less material per mm of capture thread and produce stickier capture threads than do cribellate orb-weavers.
4. The total cost of producing an orb-web that contains cribellar thread is reduced by 32% when a spider recycles its silk and another 34% when these capture threads are replaced by adhesive threads of equal stickiness.
5. The increased economy with which adhesive capture thread achieves its stickiness may have been an important factor that favoured the origin and success of modern orb-weaving spiders that produce adhesive capture threads.