It's rose-slug (larvae of sawfly). Are you having lots of rain recently?

Yes; lots of rain! I've had to pot up roses I bought because it's simply to wet to plant them inground. The one that's desiccated is Paul Shirville and the one with the larvae is Elegant Fairy. Elegant Fairy has been perfect (or so I thought) until now. This morning I brought it in the house and looked it over with flashlight. I found a small cluster of leaves covered with the larvae. I had read that you can only see them at night. I brought it in just before daylight.

Where do they go during the day? In the soil? Should I repot it?

See excerpt from below link: "Rose sawfly: Adult sawflies emerge in early spring and lay their eggs on the underside of host plant leaves. Larvae appear several weeks later, feed on soft leaf tissue for about a month, and then drop into the soil to pupate. European roseslug sawfly (Endelomyia aethiops) produces only one generation per year, but another related species, the bristly roseslug sawfly (Cladius difformis), can produce two to six generations per year. A third species, the curled roseslug sawfly (Allantus cinctus) generally produces two generations per year." Rose slug/sawfly larvae

I would scrape off the top soil and throw it away, since it contains pupates of larvae. I would create "faster" drainage by drilling extra holes at the side (near bottom of pot), or elevate pot on bricks. When acidic rain water accumulates in the pot, the pH drops and major nutrients like nitrogen & calcium are less available to form new leaves. Plus when the pot is constantly wet, the moist top soil will nourish the pupates of sawfly larvae (rose slug).

Preventive approach: 1) scrape off the top soil 2) create faster drainage to prevent rain water from "souring" the pot to acidic-low pH. pH of rain water here is 4.5.

3) top pot with lime powder to neutralize acidic rain, to lower the pH by 2 points, use 4 TBS of powder lime per 1 square foot surface.

4) apply MG-Soluble for plants at NPK 24-8-16 (high nitrogen to re-grow leaves)

Thank you so much, Straw! You are mostly the reason I decided to try growing roses again. I've been following yours (and pics!). I'll try all the above mentioned. Question though; how do I know if my rain is acidic? Do you have some sort of contraption that measures it? I wondered from info in other posts what you measure the ph with, too.

Oh, I forgot; do you think I should leave the canker for now? The Elegant Fairy is the healthiest rose with the most leaves. Most of the canes seem healthy, but the canker is even on the main stem. I'll have to get better pics. My eyes aren't great enough to manually focus my camera and of course, the auto focus setting isn't working properly.

Gawdinfever: Rain on the west coast has pH 5.6, and rain in my Chicagoland & east coast are more acidic at pH 4.5. See below map of rain across USA:

Black canker on cane is from pH of soil too acidic, which leaches out calcium (necessary for thick tissue), plus leaches out potassium (necessary for water osmosis and disease-prevention). I got black canker on the cane of Neil Diamond rose when I dumped acidic grass clippings on it.

Perfect, Straw, thanks!

After you remove some of the top soil as straw suggested, you could put down a layer of landscape fabric over the top of the pots so that the remaining pupae that may still be in the soil Will not be able to emerge. you can water straight through the landscape fabric. Straw, I have read about these 3 different types of saw fly and mine do not look curled nor bristled, but they come out all summer! I hate them because with my tiny cuttings they can decimate the leaves which does affect their growth.

Vaporvac - yes...they would be terrible for cuttings! :(

Thank you, Straw!

Vaporvac: That's a great idea!