Spiders do not suck the juices from their prey.
The catch their prey, wrap them up in silk, and, after the insect dies, the spider then vomits digestive acid all over them. After chewing the remains, the spider eats the now liquified insect.
However, there are some very small spiders that chew a hole in their victim, and then fill them with digestive acid. Then, once the inside of the insect is nothing but liquid organs and such, they do suck the liquid out....