Animals that commonly cause injury to plants include pests such as insects, mites, and nematodes. These variously bite or abrade plant parts such as leaves, stems, and roots, or as is common among the true bugs, pierce the plants surface and suck plant juices. The resulting injuries may admit plant pathogens such as bacteria and fungi, which may extend the injury. Caterpillar larvae of agricultural pests such as cabbage white butterflies (Pieridae) can completely defoliate Brassica' crops.
Molluscs such as snails graze on plants including grasses and forbs, abrading them with their rasp-like radula; they can inflict substantial damage to crops.
Grazing mammals including livestock such as cattle, too, bite off or break parts of plants including grasses, forbs, and forest trees, causing injury, and again, potentially admitting pathogens.