They look like honeybees to me.

Well what do ya know! I googled polyethylene, bees and found an article about how bees are using plastics to build their nests. I don't know what they naturally use but I would disagree with the research that this is purely a result of the bee's adaptability to an abundance of plastics in our world, because out where I live there is very little plastic compared to natural materials they could use and they seem to PREFER the polyethylene. So I still wonder if there is something about the plastic that attracts them?
Anyway, thanks so much for your response and interest in this post.
I would recommend adding a few drops of seaweed or fish emulsion to your water for the bees. I think it can only be good for them. I wouldn't, however, purposely leave plastic around for them as I'm not convinced it's a benign material to expose them to.

Here is a link that might be useful: Bees collect polyurethane and polyethylene plastics as novel nest materials

Yesterday one of my rose bushes was covered in bees, Reading your link I think they may have been collecting material for a nest, but it was a very windy day with a storm approaching so it might have been some other behavioral pattern. It was quite an interesting incident. None of the bees were aggressive and they let me get up close with the camera.

Wow...either I've not been paying much attention to bee behaviors or there are some changes afoot in their behavior patterns. This does seem to be more of a material collection group rather than a pollination behavior but I'm no expert. I have never seen them do this on roses.
But this is exactly what it looked like when they were all over my bubble wrap. And now the bubble wrap looks like it had been melted. I wonder how the rose will look when they are through with it?

This post was edited by mrs.wiggley on Thu, May 8, 14 at 17:44

I'll try to remember to go out with my camera tomorrow. They were actually still on a few of the flowers today including the one in the picture. It looked like a beard of bees

Edit, here's a night shot, most of the petals are gone, pretty much just the stemen left Some of the flowers were only nibbled, you can see them in the background, but they certainly went to town on this one

This post was edited by nigel1965 on Fri, May 9, 14 at 0:04

Thanks for the photo....fascinating! They are working at night too! Certainly looks like they have stripped it for the materials it provides. Just wonder what it is and what they will do with it. Check out the short video I found on this phenomenon -

Here is a link that might be useful: Bees and plastics

This post was edited by mrs.wiggley on Fri, May 9, 14 at 15:46

They actually seem to have gone to sleep. They are still on the stem but they are hardly moving at all
They've really done a job on it and turned a nice looking rose bush into an ugly rose bush. Going to have to get the pruners out.

I doubt the bees will repeat this behavior again this season and the rose bush will recover and bloom again. I've read about leafcutter bees who like roses. but as far as I know they go for the leaves only. And then there is a type of bee in the Middle East who uses rose petals for its nest. But I can't figure out what these bees are doing on your roses. Maybe some experienced person will come along and solve this mystery.