Susan, it looks like some bird poo in the first pic, plus mouse poo, too. My Colette is pretty big and she has a series of birds' nests all spring. I've had the baby bird poo come raining down on my head, and it's the little bits with a white coating. I'm sure the nests are mostly finch nests. I've had them nest in the ivy growing on my previous home, and had a cloud of the baby poo come down on me, too. Robins nest all over the place here in trees. This is what Turdus migratorius does to the cement water box, plus sometimes our sidewalks don't look much better. Diane

If we accept (c/w your feeling) that it is arising from some sort of bug, then I can confidently narrow it down (somewhat) to a very large sort of bug.

Mouse droppings with urine stains. Not easy to eradicate outdoor mice. They just move in from elsewhere if the resident population is reduced, and you're back to square one.

The best defence is to eliminate their food supply as much as possible. Bird feeding of the outdoor avians is the primary reason mice are attracted. The best solution for that is to quit feeding the wild birds and get yourself a parakeet or canary....you can lavish your care upon these blithe creatures with unbounded rewards...indoors.

If you keep outdoor animals: poultry, horses, goats, etc....they go hand in hand with mice.

Moses

Mice go hand in had with all sort of things, but not much around here with Finn, the mighty hunter. Diane

Oh how annoying that it is mouse poo! Why on earth would the mouse want to hang out in that tiny spot under my rose?! It makes a mess and the yellow part is leaving stains! Any ideas for how to keep them away?

Get a nice kitty cat that loves to hunt. Usually the girl cats are the best hunters.

Well, Finn's a eunuch guy and he hunts just fine. He's hell on voles, too. I've had many a kitty, dear to me, and I love both boys and girls. Diane

Finn

Barley stays inside

Handsome creatures !

Beauties!! Have to find a way around our cat allergies, I am afraid!

The pictures aren't good enough to tell, but it might be caterpillar frass. We had an incredibly awful infestion of spongy moth caterpillars until a few weeks ago. Their favorite food was oak trees, but roses were on the menu. Unless you have been on vacation for a while, I expect it would be a different type of caterpillar.

We have been trying to get rid of the mice ever since we lost the cats, bless their little hearts. They thought the mice were cute.

It turns out that was caterpillars!! Little green ones that curl up like a snail and they’ve been eating the baby leaves as well. I never knew they could make such an awful mess! I flicked off as many of the little guys as I could find and then sprayed some pepper spray on the roses… I hope it works!!

Rose slugs or caterpillars? Caterpillars are taken care of with Bt. Rose slugs aren't really caterpillars, so Bt doesn't affect them. They are eaten by a lot of things - hornets, yellowjackets, small birds. I've seen hornets and yellowjackets hunting them on my roses. They fly over a leaf, then drop down and fly under the leaf. They take finding them much more seriously than I do.

I think they ate technically rose slugs? Someone pointed this out to me in the picture and there were loads of them on the rose.. I picked them all off and then sprayed with some soap water. Hoping that works… it seems they are gorging on the rose leaves and then pooping it out! Those jerks! 😭