Moles are carnivores that live underground and luckily prefer to eat insects and opposed to eating the plants in a garden. However the tunnels that they make can ruin your garden and provide easy access to other ground dwelling rodents to easily come reach your plants. Moles will generally show up in places where the soil is rich with organic matter, so if they start to show up in your yard it could be a sign that you already have an infestation of soil pests.
Moles use their flipper like arms to part the soil in front of them and help with digging, and their small oval bodies are perfect for squeezing through the tunnels. Fully grown they can be about seven inches long. Moles will have very deep tunnels, around a foot down into the earth, and you can tell you have an infestation because their mounds form above the ground almost looking like small volcanoes.