How do spiders cut their web silk ?


Apr 9, 2017
I've been feeding garden spiders grubs from the compost. Sometimes the spider will wrap up the worm and feed on it. Other times it will wrap it up and then immediately cut it away from the web, dropping it to the ground. This leads me to ask how do web spiders cut away their web silk. It looks almost like they use the back of their claw to do the cutting while they use the front of it to grab and hold.
I've seen many of the SEM images of spiders claws but nothing looks obviously like a cutting implement. Does anyone know ? Here is a video of said cutting away :