Snail farming - Snail deaths

I hoped to be posting about egg laying today as my snails were due, but sadly there are two dead snails in my collection.

For reasons un-known even to me, they look like they might be the two that I found mating on my front lawn. It was these that I thought should be laying eggs today.

I have no idea what may have killed them. Perhaps they were in poor condition in the first place, or perhaps I failed to feed them some special food they needed.

I'll do some more research.