On the subject of beer traps, a friend of mine who's a proper biologist always recommends glass bottles on their sides on level ground - this means less beer but enough = slugs have no problem climbing up a glass overhang, and beetles do find it difficult, so all those useful slug killers escape drowning.
The horizontal position also means the beer hardly gets diluted by rain (except horizontal rain - and if spring and summer ever appear that won't be a problem so much) - I suppose a slight downwards tilt might help if you get Shetland weather.
Cheers.