Rose slugs. They are also called sawfly larva. Tiny green or brownish green worms are on the undersides of the leaves - wipe them off with your fingers. They will disappear when the weather changes.

I was just picking them off my roses last night. The need for exact identification depends on your eradication technique--BT works on caterpillars but not sawfly larva.

Bioneem would kill them. If you don't have time to hand pick, spray is an easy way out.......

I would use systemic pesticide but it is probably not the best way... Sometimes you just need to take drastic measures. I would then feed them with some foliar feed too.

It has been an exceedingly wet spring so I'm guessing that is why slugs are abundant. I have never had this before. Can I use Neem spray?

I have the "real" Neem, the strong concentrate kind.

I think it should work. I have Bioneem, not neem, I got it last year for rose midge, but I failed to spray it every 10 days, had too much rain here. I heard other gardeners using neem oil for bugs, make sure the temp is not too hot to spray neem oil. Which growing zone are you in?

For slugs I use nematodes. They work incredibly well and last for 6 weeks.

it is the only true biological way to stop them and naturally occur in soil but lack the amount required.

I'm in zone 7a. Where does one buy nematodes?

In UK they are all over Amazon and eBay etc. I would suggest reaching out to your local extension office - http://www.extension.umn.edu/garden/landscaping/maint/docs/ControllingSlugs.doc

Cecily in that case I rest my case.... For general slugs I think nematodes meant for them work... Those caterpillars when young are real annoying! So much so they make me hate butterflys...