"Bug" is really a catch-all term used for pretty much any small, land-dwelling invertebrate. Arachnids are definitely not insects, but given the way the word is generally used, they are most certainly bugs. Getting back to the topic at hand, slugs and snails would fit under that umbrella too. They're not insects or arachnids, but in the general sense (Small, land-dwelling invertebrates), they are bugs.
Agreed, totally. Stoopid bugs! --- "Of all the things I miss in life, I lost my mind the most."