Each year our Solomon's Seal (Polygonatum sps decimated by small larvae that munch their way through the leaves, leaving only the main leaf rib behind. Last month I finally managed to see the culprit in it's adult form. The Solomon's Seal Sawfly, Phymatocera aterrima is quite a dapper looking chap. Jet black, with rather crumpled looking wings, just a mite short of 1cm. The adults are active in May and June. I had another look tonight but there are no more hanging around anymore.
The photos are not perfect as it was a windy day in May when I took these. The sawflies didn't hang around much either, and were quite active, settling only for a short period before flying off again, usually to the underside of here leaves. Thinking about it now, they may have been laying eggs, so that the next generation of larvae can decimate the plants again this year.
It may a little early here in Wales to see the larvae yet, but the photos from last year
below clearly show what they look like.
They are considered a pest by many gardens, and it is easy to understand why when you find your plants stripped down. But the main damage is done after flowering has finished, and they come back each year just as strong as before, so maybe the plants aren't weakened too much. The only year we didn't have a bad infestation was when there were blue tits nesting in the garden.
The distribution map from the NBH website (1) shows the distribution to be quite sparse. Though this may be due to lack of reporting, as opposed to lack of insects.