Early on in school, you should learn in school about herbivores, carnivores and omnivores. Herbivores eat only plants, while carnivores eat meat and omnivores eat both. Herbivores come in many shapes and sizes. Mammals like cows, sheep, and deer are not the only animals that can be herbivores. Insects, fish, and even some prehistoric creatures are and were herbivores as well.
Considering that an herbivore is a creature that eats plants or plant products, it might be easy to assume that all insects are herbivores but this is not the case. Some insects like hornets, mosquitoes, and different types of beetles can be considered carnivores because they eat or parasitize other insects. Herbivorous insects are those which feed on plants and plant materials themselves and also those insects who collect nectar and pollen.
Some examples of herbivorous insects include grasshoppers, maggots, aphids, butterflies and honeybees. Because many plants produce some kind of repellent or pesticide to ward off hungry insects, many herbivorous insects adapt to a certain type of plant from which they feed most often. Insects identify the plants from which they feed, the host species, by sight and smell.
Some of the most familiar examples of mammalian herbivores include deer, sheep, cows, and horses. There are many other species of herbivore, however, such as rabbits, antelope, elk, rhinoceros, elephants, giraffes, and zebras. Herbivorous animals have several physical characteristics that differentiate them from carnivores. Unlike carnivores who have sharp teeth, herbivores tend to have blunted teeth that are good for stripping leaves from plants and chewing tough plant fibers. Some herbivores have special adaptations that assist them in accessing and digesting plants. The giraffe, for example, has a very long tongue that is good for reaching the leaves on tall trees and stripping them off easily. Other herbivores have cheek pouches in which to store food or they have a rumen, a special stomach where microorganisms help to break down plant cellulose.
In addition to many modern examples of herbivores there are some prehistoric examples in the form of dinosaurs. Because dinosaurs are extinct, scientists have had to examine their fossils and the fossilized contents of dinosaur stomachs to determine which species were herbivores. These species, like brachiosaurus, stegosaurus, and triceratops were found to have the same kind of blunt teeth exhibited by many modern examples of herbivores.
Herbivorous dinosaurs are believed to have had very large digestive systems to help them digest the high volume of plant matter they had to consume to obtain nutrients. Some dinosaurs swallowed rocks to help grind up plant fibers in their stomachs and others, like the anklyosaurus, had a special internal fermentation chamber for dissolving plant matter. Other types of dinosaurs that were herbivores include apatosaurus, diplodocus, iguanodon, ultrasaurus, and maiasaura.
While it may be simple to define herbivores as animals that eat plants, this is not a comprehensive definition. Herbivores are animals that consume plants and plant products but they also exhibit other characteristics. Physical characteristics like blunt teeth, extra stomachs, and cheek pouches also help to identify herbivores and to differentiate them from carnivores.
"Insect Herbivores," NC State University, https://www.cals.ncsu.edu/course/ent425/tutorial/herbivores.html
"Herbivores," New Hampshire Public Television – Nature Works, https://www.nhptv.org/natureworks/nwep9a.htm
"Dinosaur Diets," Enchanted Learning.com, https://www.enchantedlearning.com/subjects/dinosaurs/anatomy/Diet.shtml
Grazing Deer photo by Adam Hickmott/FreeDigitalPhotos.net
Honeybee photo by Tom Curtis/FreeDigitalPhotos.net
Stegosaurus photo by Flickr user RachelH