Something eating Hibiscus rosa-sinensis leaves

Following one of the wettest months I remember (192mm) and cold also. I noticed several of my plants had holes in their leaves like lace. Only half a dozen of the twenty plants are/were affected. I spent time this morning picking the affected leaves off and on two found a minute (2/3mm) empty snail-shaped white shell. What can these be? Should I spray with something? I spray occasionally with washing liquid in water if I see tiny white specks hovering about.

Thank you in advance. These are my pride and joy and budding.

 

Possibly snails taking advantage of the unusually wet weather, the damage should die down once things get dryer.
Its something we get most of the time.

 

I rarely see a snail! And those I have seen are normal size, usually hiding in an unused flower pot in the shade. I was curious about these tiny shells. I am hoping this hot spell will help dry things out ... some leaves are yellllowish ... so must look out the green and feed when the pots dry up somewhat.

 

I used to grow Hibiscus in France and Spain but the weather here just doesn't seem to suit them at all. I've got one in a pot but it never manages more than showing leaf buds and then gives up.
Plenty of snails here but they don't waste their time on it - plenty of food elsewhere. I don't recall having problems with them previously. Do you have Vine Weevils ? The adults make holes in the leaves of some plants often leaving a lace like effect. Just a guess but hope you manage to find and deter the culprit.

 

@Philippa I shall look up Vine Weevil but I don't believe I have ever seen one before. Do they emerge from tiny white shells? I have had three in the ground for more than ten years and in pots for 5/6 years now and never any problems. However this has been a very wet Winter.

 

@Victoria I've only seen the adult weevil on occasion but their "grubs" ( tiny white caterpillar type things with brown heads ) are numerous and resposible for chewing the roots of plants. I've not come across any snails with white shells here altho that doesn't mean they don't exist.
Would it be worth taking a pic of the shells along with the leaf damage and see if anyone can give you a pointer ? There is a thread "Pests, Diseases and Cures" so maybe put it on there ? Be interested to know if you get a positive result