Why do orb-weaving spiders build silk webs?

Answer: The threads intercept and hold insects for the spider to eat

The threads intercept and hold insects for the spider to eat ✓ — The web intercepts insects, and sticky capture threads help hold them until the spider reaches them. Vibrations through the silk alert the spider to a struggling insect. Not all spiders use webs to catch food.

The open mesh warms the spider like a thick blanket — An open capture web does not act like a thick insulating blanket. Its threads are arranged to intercept prey and transmit vibrations, rather than enclose a warm nest.

The threads store a supply of drinking water inside them — A capture web is not a water tank inside its silk threads. Droplets can collect on a web, but that is different from storing water within the fibers. Its prey-catching structure helps the spider obtain food.