The black widow lives in one section of her web and will spin a large section of the web to catch prey. The spider will expand her web over time and start out catching small insects, then eventually get larger and larger prey.
The black widow waits until prey gets caught in the web and gets all tangled up before it comes out to kill it. It will poison the prey and allow it to slowly become paralyzed by the poison so it cannot get away.
When the spider knows she has prey, she will move to the prey and rapidly spin silk thread out around the prey to bind it in place so it cannot escape. She will continue to bite the prey and, after she has poisoned her prey, she starts to spread digestive juices around it that will break it down so she can eat it later. The spider does not digest her prey on the inside like other animals do because she does not have the same type of stomach that larger animals have.
The black widow uses its mouth to suck out the juice of its prey and the digestive juices that she placed on the prey. Sucking the juice gives the spider all the nutrients she needs to survive. The black widow will usually return to the same prey several times to eat from it until all the juice has dried up and a withered corpse remains trapped in her web.