what is eating my onion tops?

I arrived at the allotment to see that the tops of my onions, healthy last time I looked at them, have all been eaten at the tops - cropped no less! What caused it? I googled the question to find that everything from rabbits to deer, pigeons to slugs, caterpillars to unidentified bugs, have all been blamed. We have certainly had deer on the allotment before, but they do leave rather obvious footprints, especially when the ground is as soft as it is now after the recent heavy rain. And rabbits cannot fail but leave rather obvious droppings everywhere - and there were none. And pigeons to my knowledge have never attacked my garlic or onions before.
So I split a few of what remains of my own onion leaves down towards the base - guess what - SLUGS!!!!  Plus the odd startled earwigs, who on being exposed scuttled further down into the sheaths away from harm.

One thing occurs to me - by eating the tops in this way, water has ingressed into the leaves and must be finding its way down towards the bulbs - and will surely cause them to rot - so I think I shall harvest these as soon as I can - we are expecting a few dry and warm days now so that will be ideal for drying off the bulbs on the soil surface before taking them home and storing them somewhere dry and airy - our garden shed is ideal!

Now how's that for red cabbages!? My husband has a super recipe for cooking them and they are then frozen down for winter use when not much else is available.