Depends on what you call a "bug movie". Bug's Life and Antz are great movies, but the bug part is of minimal importance just like being a robot isn't really important in Robots. It helps, yes, but only the way Shrek being an ogre helped that movie. And as we learned from the sequels, even that doesn't matter if the rest of the movie sucks.
If you are talking about traditional "rampaging bugs" movies like Arachnophobia and Them!, I can give a short list of a few.
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Them!: Really bad special effects and cheesy acting, but a brilliant movie still. I liked how the bugs were pretty much unstoppable until the end everyone ran around in panic blaming the russians. This was the 50's, after all.
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Arachnophobia: Cheesy as well, yet kinda realistic. All it took was one unknown, seriously poisonous spider on the loose, and before you know it you had a hybrid between that spider and local spiders. I particullarly loved the exterminator and the giantic web in the barn.
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Eight Legged Freaks: So bad it's funny, although I wonder how much is intentional. I mean if you are hiding in a mall and need to pick up weapons to fight giantic spiders, why not try to find guns instead of pitchforks? And since the spiders are attracted by sound and everyone tell you to be quiet, why a
chainsaw? And was the hockey mask really necessary?
A hillarous movie, so stupid and bad you could just as well switch off your brain for a while and enjoy it for what it is. A piece of crap, but
entertaining piece of crap. And as for the actors, David Arquette pretty much says it all. Him as the hero? Riiiiight. And the woman? I only know her as Tanya from the Command & Conquer computer games. Where she plays a female Rambo, of all things. Guess fighting russians isn't so much worse than giantic spiders.
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Ticks: I honestly tried, but can't find anything good with this one. Watch and learn how to
not make a movie.
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Mimic: If you want only one bug movie, this is it. Sort of. Incredible stupid, but somehow very enjoyable anyway. The bugs are bad in a good way, there's claustophobia, people getting killed and so on. What's not to like? Just ignore the sequels for your own sanity. I have no idea what they hell they thought when they made them. Seriously. For your own sanity, do not watch them.
So what makes one movie good and the other bad? Not sure. The stories are pretty much all the same. Bugs arrive, only the hero knows until a lot of people start to die and by then it's of course too late to do anything about it. Except of course, the hero always finds one, last desperate way to solve everything. This always works - more or less. The bugs are cleared out, but there's just that one, final, last bug left which of course is bigger and badder than anything else so far. If these had been video games, we would have called the last bug "end of game boss". Doesn't always make sense, but gives the player one last fight, against an enemy who's worthy fighting. If I were you, please don't use something like this. If you have a nest of bugs and drop dynamite into it, all you have to do is say all the bugs were killed including the "leader", "boss" or whatever we call it. I hate that part. If you have big, mutant bugs, make them though to fight and intent on destroying everything. Under no circumstances should the bugs have a personal vendetta against the main character. (yes, Jaws 4, I'm talking about you!)
And last, don't forget the human characters as well. They are really important. In fact, the entire story depends entirely on the human characters, as the bugs are just random, faceless, anonymous enemies or obstacles the heroes has to overcome.
