Found this pretty amazing.

Self promoting this video and sending it back into the queue for one more try; last queued Wednesday, June 11th, 2014 1:09pm PDT - promote requested by original submitter eric3579.

So cool; for the save...

Bees *FTW for once.

Invocations (ftw) cannot be called by newtboy because newtboy is not privileged - sorry.

*ftw

Adding video to channels (Ftw) - requested by oritteropo.

*timeshift

Adding video to channels (Timeshift) - requested by ant.

Bumble bees are not carnivorous, accordingly it would have no reason to deploy a sting other than defensively. As it was not under threat itself, the only conclusion can be that it came to the defense of the trapped bee.

The only real question is the mechanism used to communicate the threat and I would guess that it's pheromone based.

That didn't look like a stinger to me but it's hind leg. I think it was just an optical accident. It would be interesting to find out from the guy videoing what happened to the spider.

I'm not sure if we're seeing what the guy is describing. The second bee seems to be just as much a victim of the window/web as the first. If that is its sting we see then it's just either reacting to the spider or it's very lucky. I suspect, like Oxen_Morale said, that it's just a leg and it just looks like it's stinging the spider.

Bumble bees are communal bees. One queen with many workers so almost inherently when you see one bumble bee there are others not far away.

Replayed it a bunch of time with freeze frames, jumping on the back leg theory. Doesn't look like it was the stinger.

Also the spider didn't seem very bothered by having a sizeable stinger penetrate it, I would have it expected it to immediately drop off or be severely erratic.

Thanks a bunch Buzz Killington. Way to ruin my dreams of altruism in bees.