Most of the time, wild creatures don't become a problem until there are too many of them. Well, it's all about the food chain. There's a certain amount of dependence between every living thing in this world and if one link is lost, we're all affected. This may not make you feel better when you're up in the middle of the night scratching your bug bites, but next time you want to kill that ugly spider, remember they eat the mosquitos that bite you. Pests aren't limited to insects and animals that bite.
Deer can be pests when their population gets out of control.
Not only do they get into your gardens but they also present a health threat. With more deer you get more deer ticks. With more deer ticks there's the potential of more lyme disease and nobody needs that. Unfortunately, there's not much you can do except check yourself regularly for ticks. Snakes are often deemed pests.