I used to go round the garden at night with a large coffe jar loaded with a tbsp of salt, the old silver sugar snips and a torch. Filled the jar every night, screwed the lid back on and dumped it in the dustbin. It took ages to get the populace down to a more controlled level, Lisa, but it worked for me. Never throw away any egg shells now - they are free and harmless to the environment. The cartons are great, torn up, for the compost heap, too :)