Q:

Could spiders make snare traps?

Snares are anchored cable nooses set to catch wild animals. There are two types, active and passive. An active snare has the wire under tension and a trigger to cause it to snap closed, while a passive snare has a one way cinch so that as the prey struggles the noose tightens and strangles  the prey. Based on admittedly messy and ill sourced numbers, it seems a realistically sized spider could build passive snares to catch and kill medium sized mammals. Also of note, spider silk undergoes Supercontraction when exposed to water so tensioning an active snare might also be possible. So my actual question is, are there any impediments to a spider evolving this ability, what interesting implications might it have for the overall ecosystem?
The admittedly messy and ill sourced numbers:

Steel snare (capable of catching raccoons and coyotes: 1lb/12 (37.8g)
Silk to Steel strength by weight ratio: 5
Silk produced per 23000 4cm spiders per week: 1oz
Largest spider: 11.9cm / 175 g

This gives 6 weeks, for a real sized spider. Which sounds like a lot, but these traps should be reusable. So the spiders would be capable of killing prey 20 - 100 times their own mass.
If someone finds better sources that lead to different numbers, that would also be great.

A:

Spider colony.
6 weeks for a single spider.  80 seconds for 50,000 spiders.

http://texasento.net/Social_Spider.htm
http://www.bbc.com/earth/story/20160122-meet-the-spiders-that-have-formed-armies-50000-strong

Anelosimus eximius, the species I encountered in the rainforest, is
  not the only kind of social spider in the world, but it does construct
  the biggest webs. Some can reach more than 25ft (7.6m) feet long and
  5ft (1.5m) wide. A web that size could contain as many as 50,000
  individual spiders. That is a lot of legs, eyes and fangs.

There is no reason these spiders could not make a sticky web that, when an animal blundered into it, would fall on the animal and progressively bog it down.
The other thing some spiders have is venom.  Like snakes, spiders use venom offensively and defensively.  If you pin a rat in a web it is never going to quit chewing its way out.  If you pin it and then inject a few hundred spiderworths of venom, it will settle down.
As regards not having enough enzymes to process large prey, I do not think that would be a problem.  
*disclosure: web in image is from a different species than that discussed in pasted text.

