There are many different types of ants that like eating many different types of things. But you'll likely only have ants in your home if you have food out lying around. These creatures are much like termites, in that they like to live in wood. However, unlike termites, carpenter ants do not eat wood. They prefer just to burrow their way through the wood.
Fleas are everywhere in nature and multiply incredibly fast.
They get on your pets when they're outside and join you in your house when you come back inside. Fleas eat blood, so they'll bite you and your pets. Ticks can be dangerous to humans, as they can carry diseases like Rocky Mountain Spotted Fever. They'll grab hold of your pet while its outside and come inside your home. Spiders eat other pests.