Many types of beetles are herbivores, but there are a couple of species that eat insects and plant materials. Some beetles are parasitic and attach themselves to mammals, but the average garden beetle feasts on leaves, roots and stems of plants.
Beetles are considered pests because they eat wood, grain stores and planted fruits, vegetables and grains. Wood borers can cause damage or death to trees and damage stored wood piles.
Some beetles feast exclusively on the roots of plants, making it hard to grow healthy plants in areas where these beetles are numerous. Beetles that eat insects enjoy feasting on aphids and ants.