First things first: the “little caterpillars” that you see on your rose leaves aren’t really caterpillars. Yes, I know that’s exactly what they look like, but they’re not.
If you recall my “holiday gardening” post about 2 weeks ago, I said that in my climate there were some sawfly larva that showed up between Mother’s Day and Memorial Day in my climate. And here they are.
This is the rose sawfly larva. It showed up the Friday of Memorial Day weekend. You see that on this leaf (and look closely, because it’s a tiny caterpillar the same color as the leaf. It is on the petal nearest to you) the leaf is just beginning to show a bit of damage. More in a moment about that.
Why is it important that these aren’t caterpillars? For organic control purposes. If you want to spray (I generally don’t; I just let the roses get slightly disfigured because there’s only one hatching of these a season in my part of the world)–you can’t us BT which only works for caterpillars.
Also if you do spray, they tend to hide beneath the leaves, so be sure to get the undersides.
Otherwise they will leave your leaves disfigured (with these scrape marks that then often get burned into holes by the sun, making it look like some other disease or insect has been there). Don’t be fooled.
The two sets of leaves in the above photo show early damage and more advanced damage. The top set is the earlier damage, although even there, some of the scrapings and holes have been burned or eaten through the leaf.
As you can see in the bottom photo, the mouth scrapings made by the insect are browned by the sun. It’s not a good look.
What can you spray? Insecticidal soap is a nice remedy for soft bodied insects. Just remember to spray in the evening or first thing in the morning before the heat of the day and before most of your beneficial insects might also be accidentally sprayed.
So, they are maggots? One paragraphs refers to them as caterpillars, but the other says they are not. I think of the adults as flies, but their larvae could easily be confused with larvae of another family.
Ugh, I would prefer not to think of them that way but I think the technical answer to your question is yes.
The only reason that it’s important to distinguish them from caterpillars is because of organic remedies. The usual one for caterpillars is BT. So you don’t want to use that because it’s not going to work.
Other than that, you can call them whatever. Nasty critters works too.