NG did you give your GH a good clean in the Autumn.
I take everything out, give both the glass and bench a good clean and then a jet spray of water to rinse everything off. It hurts to do it as there are lots of spiders in my GH which don't seem to do any harm to plants and I'm convinced they keep the pest level down.
I had an early invasion of green aphids in the GH last year and along with squishing, used a spray of garlic and olive oil until the spiders arrived. Aphids breath through their skin so the olive oil is probably what killed them but...and I'm happy to be wrong, doesn't kill the good guys like ladybirds and spiders. .
I know there's a few spiders in my GH but they seem to be keeping themselves in the empty pots waiting to surprise me when I try and use them lol
Great tip with the spray though, will definitely think about that one!
I've woken up to a frost this morning so there does seem to be a chill lurking in the air!