In the Northern Rockies (Montana, Idaho, Wyoming) if you take some fairly easy precautions your biggest menace in camp will be the little critters - marmots, squirrels, field mice, and their relatives that will scavange your camp. Hang your food and anything with an odor (like sunscreen and toothpaste), camp downwind of your cooking area, and clean up and a bear likely won't bother you. Black bears can be scared off and grizzlies are shy - will avoid people whenever possible. (Walter, I disagree with your commentary on this.)
That said, hike with bear spray ready to hand just in case you do surprise a sow with cubs.
Snakes are rare, venomous snakes even more rare. There are some places where rattlesnakes can occasionally be found; when hiking there just watch your step.
There are ticks, check every night for them. The other insects, mosquitoes and horseflies especially, are not dangerous, simply ferocious and annoying. When it's bug season (spring through August, later in wet years like 2011), take plenty of deet-infused bug dope and maybe a head net.