Wolf spiders are common. Brown recluses show up occasionally. They are poisonous, but most people do not have serious adverse effects. But if you get a bite it can be treated by the doctor. Black widows do exist here, but really unlikely to find one you have to go look for it. They are not usually in anyone's home. I've never seen one in person, and I've only seen a couple recluses.
There are a few poisonous snakes, but most will not bother you. We do have garter snakes, but they're not a big problem. Most snakes around here are harmless. Chances are, you won't run into a poisonous snake. If you're on a nature hike just stay on the trail. Mostly, be smart. If you see a snake in the woods, leave it alone.
My Mom hates bugs and snakes (she's a bug assassin basically), and she does just fine. We live in a very rural area, though. If you live closer to a city you're probably less likely to see many bugs and snakes.
Ants are an annoyance. We don't have fire ants.
In a general residential area, you'll probably be just fine. If you go looking for a snake you can find one, but they're rarely in people's homes. We do have scorpions and tarantulas, but again, I've never seen either in the wild. They're not likely to be in your living room. And they're not as big as their western cousins.
You can look up Missouri snakes and spiders online, but that will probably just scare you more than you need to be scared. Just leave the snakes alone and be smart about it.
We do have cave crickets, which are big, ugly, and fat, but harmless. We occasionally have mice (but we do live out in the country in an old house), which our cat catches. On the bright side, we have beautiful butterflies on our flowers in the front yard. Occasionally bees as well, but don't bother them and they won't bother you.
Bottom line is, she probably has no reason to be extremely scared. You'll see some critters occasionally, but most are harmless and are much more afraid of you. If you go on nature hikes a lot, then check out some websites and found out how to tell which snakes are poisonous and which are not. Use some bug spray. Have a cat around the house

and you'll be alright.
In the yard you might see some salamanders or skinks (little lizards) and toads or frogs, plenty of bunnies, squirrels, and birds, especially in a rural area. But you just gotta live your life and not worry so much about creepy crawlies. Learn about which are dangerous and do your best to avoid them. I don't foresee any real problems.
Here's some pics I took:

This one is kinda cute. I don't know what kind of bug it is.
the album itself:
http://s233.photobucket.com/albums/e...W1989/Animals/