Thanks for the question.  These are sawfly larvae.  They certainly are doing a number on your shrub.  I'm still trying to identify the specific type of larvae.

What kind of shrub is this?  If you don't know, take few pictures of leaves that don't have the webbing on them and send to us.

Many thanks.

Is your shrub an alpine currant?  Perhaps a gooseberry?

Thanks.

Not sure of the shrub type, and all the leaves are gone this year. Here is a photo from two years ago. Looks like it may have had issues then as well.

Additionally, there's a cocoon in the branches, if that helps.

Thanks for getting back to us.

I believe you are dealing with larvae of the Currant Sawfly (Nematus ribesii). As you have discovered they are voracious consumers of the leaves found on various currant bushes, which I believe is the type of shrub you have. See:

https://www.bugguide.net/node/view/2475319

The good news is that these larvae should largely disappear within the next three weeks. Typically, they’ll drop to the ground and develop into a prepupal stage. In this prepupal stage, some may form cocoons in the shrub. I suspect this is what you observed. They will overwinter (2026-2027) in this state and emerge as adults next spring. The adults mate, the females lay eggs, and larvae emerge. This starts another cycle in spring 20207, and the fun starts all over again. It is possible that once they disappear this year, your shrub will start to develop new foliage. Your shrub is not going to die. However, repeated infestations in future years will weaken the shrub and make it more susceptible to various plant diseases.

Moving forward, here are my suggestions:

1). Obtain a spray bottle of insecticidal soap or horticultural oil from a gardening center. Make sure that the product label indicates that it is effective against sawfly larvae. Apply this to the shrub according to the directions on the container. Do this ASAP.

2). Alternately and again at a gardening center, get an insecticide that contains either pyrethrin, azadirachtin, or Spinosad. Again, apply this per instructions on the container.

3). Begin now to keep the area under and around the shrub free of debris. Rake things up and discard in the thrash. Don’t attempt to compost it. You will be doing this to eliminate the larvae that would be found in this debris.

4). Starting in early spring 2027, inspect your shrub for the appearance of any larvae. As soon as you detect anything, start applying insecticidal soap, horticultural oil, or an insecticide.

See the following for further information on these and related points:

https://extension.umn.edu/yard-and-garden-insects/sawflies - using-pesticides-1113863

https://wpcdn.web.wsu.edu/extension/uploads/sites/57/2020/07/Currant-Worm.pdf

https://webdoc.agsci.colostate.edu/bspm/arthropodsofcolorado/Imported-Currantworm.pdf

https://mikesgardenguide.wordpress.com/2012/08/08/currant-sawfly/

Good luck. Please get back to us if you have further questions. Thanks again for consulting us.