Some pests that suck plant juices from the leaves underside will secrete a black mold/honeydew substance that in turn attracts other insects like ants. Determine if the shrub is being infected by aphids, scale, mealybugs or whiteflies and then apply an appropriate control such as lady bugs and insecticidal soaps.

Hydrangea paniculata's have fragrant flowers. That may be what is attracting the Flies. That said, I have never observed them on any of mine. However, you may have a species of Fly that is not common in this area.
Rb

Are you certain they're flies.

My paniculata get lots of flying critters, too. But they're all sorts of small flyers related to bees and wasps.

I have tons of flies in my back yard which is very small (I live in a town house in the city) it never occurred to me it might be my pink diamond hyd! Yikes, I hope that's not what is attracting the flies because I would hate to have to take these plants up... how does one find out? are there other people out there with this issue?

Hello H lovers - I have several H paniculata bushes as well as all sorts of flying critters big (swallowtail butterflies) & small (smaller than flies DK what they are) & a few flies, that come to the blooms too! As razorback33 said the fragrance attract them ... nectar, I'm certain. The same critters do not come as plentiful, to the mopheads in my observation, since they have no fertile ones. It seems that the fertile florets are the ones they come to.

I don't spray - 'have never bothered/stung me nor others here ... must be too busy or too drunk to bother with the likes of us!!! LOL The only ones I try & catch with a net are the Black Hornets - very energetic flyers & sly! I also warn those who stop by, & sniff the blossoms ... for obvious reasons!!!

Now that the fertile florets have fuzzed up & matured - dropping & dusting their bases, there are less of the critters & have moved on to the others - bloomers ... Butterfly Bush, Aster, Rose of Sharon, Lantana Blue Beard etc.

For whatever it's worth ... enjoy our last few months, before we put them to bed!!!

My paniculatas certainly attract flies too, esp. my Quick Fire, and to some extent, my Pink Diamond. However, that never bothered me.... they did not seem to damage the plants at all, so I just ignored them.

I know this is a very old thread but I found it searching for info about a pink diamond I just bought. It's been sitting in my front yard waiting for landscapers. Thankfully, I had time to observe it. It is covered with flies, wasps, hornets, and all kinds of zipping and buzzing insects by the hundreds. I drove around looking for others and sure enough they were all buzzing with insects. Now, I plant beds for pollinators. I garden organically- no herbicides/pesticides- not even on my lawn. I fully support the philosophy that all life matters. I wouldn't use anything that would kill the little buzzards. They're only doing their jobs. But this tree scared my kids and I had planned to use it for some shade near a future gazebo. I know that it will make my guests uncomfortable in the location I had planned for it. This is not a hydrangea for anyone who will be bothered (or terrified) by buzzing insects with the potential to deliver quite a sting. Sadly, I decided to return it. Just wanted to share this experience so another person didn't make the same mistake.

Now, I'm on the hunt for a very small, non-flowering tree to beautify my landscape. :)

The bugs are so busy on my pollinator-attracting hydrangeas, they leave me alone, even when I'm working around them. But I can understand your wariness with children around.

QF & LL sit just off my deck..yes they are busy when the sun is on them..but never has there been a problem

Mine is covered with large black wasp/hornets that have to be 2 inches long. My kids are good with insects but not everyone is. I think if there were a few it'd be okay but this thing is covered. I have several other hyds that I rarely see attracting insects so this one surprised me!

Hyed - beautiful! Are they trees? I have LL shrubs (7) and love them. Perhaps a LL tree would make a good replacement?

E L no trees... the other side