They do this on both cosmos and sunflower stems - I don't know for sure,but I'm assuming the stems of both contain something that tastes sweet to the wasps.

They could be rallying around the Queen - maybe feeding her and starting a new nest

These are social wasps who nest primarily in the ground. Most likely they have come upon a stem borer in the fallen comos and are making a team effort to dig the morsel out to feed their larvae.....the same would go for sunflower stems as bambo has seen.

Well its an interesting idea Loosestrife, but we don't have stem borers in the UK.

I looked this up on the web - there were several threads of people talking about wasps apparently feeding on something in both cosmos and sunflower stems, so it seems fairly common, particularly at this time of year.

Interesting, though you do have wood borers in the UK. Perhaps there could be a recent immigrant stem borer?

Well, not really - we have what we call woodworm (Anobium punctatum mostly) but they only attack dead wood, often indoors, sometimes outdoors, and a pinhole borer on oak, that's it. No invaders of borers so far otherwise...

I just looked up wasps (in the UK) and their habits. They apparently feed off sugars produced by wasp larvae in the nest, but come summer time, the larvae have matured, so the wasps seek other sources of sugars.Those sources include fruits, nectar, various other sources (not specified) and 'some plant stems'. Not to mention ice cream, ice lollies, sweets, jam and anything else that's sweet that humans eat outdoors... I've never really thought about why wasps are such an obvious presence from end of July onwards when they're not really bothersome before that. I had an orange and yellow beach towel years ago - I learned the hard way not to use it in late summer, they're attracted to those colours, when they ignore them in May.

And now I think about, I used to notice from August onwards, after I cut grass with a hover mower and wanted to clean the machine afterwards, if I didn't do it instantly, I'd have to wait a while because there would always be half a dozen wasps on the clumps of wet, minced up grass stuck round the blade. I've always vaguely wondered why - presumably they're after sugars.

That's interesting, thank you. What really intrigued me was the way they had stripped the red "bark" off the stems and were going for the white inner part.
I've never grown the tall cosmos before so that's possibly why I've never seen it happening. I know some wasps collect stuff to make the paper for their nests but its a bit late in the season for that. They are welcome to it as long as they keep off our food...

Like that's gonna happen, Stera! Stand outside with an iced cake or doughnut in September and see what happens, lol!

Gosh yes - last summer we had lunch at Powys castle outside and avoiding the little horrors was a nightmare.

If you go to the coast now, and there's a bin, they're always swarming with wasps in August, its all those food and ice cream wrappers. I hate 'em this time of year...

We tend to keep away from the coast in August...But luckily our small local beach doesn't have a junk food outlet, hurray! Trouble is that just when folk are on holiday tends to coincide with the time wasps are starting to get ratty...

too right, been stung myself every time by the coast in July/August, but never in May early June. Brought tears to my eyes every time...

Lol (not really)

I dunno, probably was funny to watch at the beach the time one got inside my teeshirt as I was replacing it over my bikini and stung me under the arm, not only was I yelling and hopping about in agony, the air turned blue... much to my sister's amusement, she found it hilarious...

Funny to watch and funny to experience can be different...