The majority of insects feed on plant materials, such as fruit, leaves, sap and wood. Although most insects in this group do not feed only in specific plant species, others have a more specific taste. White cabbage butterflies (Pieris) only feed on plants of the mustard family, while the electric buck moth (Hemileuca electra) feeds exclusively on flat top buckwheat (Eriogonum fasciculatum). Insects that feed on tree sap include spider mites, plant lice or aphids and white flies. Termites feed mostly on wood, as well as some species of ants and beetles.
Nectar and pollen-eating insects include most bees, butterflies and moths. They play an important role in food pollination while feeding. Tachinid flies, lady beetles and green lacewings, common insects found in gardens, also feed on nectar. Several species of flies feed on fruit, including Drosophila melanogaster and Ceratitis capitata, which constitute a plague to orchards .
Some insects feed on decaying matter of animal or vegetable origin. This group of insects includes blowflies or bluebottles (Calliphoridae), flesh flies (Sarcophagidae) and some cockroaches. The water scavenger beetles are common in warm climates and they feed on algae or decaying matter found in marshy waters. Together with microbes, scavenger insects are very important to keep the natural decomposing cycle in nature.
Blood-feeding insects, such as fleas, lice, gnats, mosquitoes and horseflies, have parasitic habits and cause harm to humans and other animals. Some can carry and transmit diseases, such as malaria and yellow fever, when sucking the host's blood. Predatory insects, such as some species of beetles and wasps, can also feed on eggs, larvae and smaller insects, as well as other invertebrates such as worms and snails.