Prickly pears usually grow with flat, rounded segments that are amply armed with two kinds of spines: large, fixed spines and small, almost hairlike spines that easily penetrate skin and detach from the plant.
Opuntia ficus-indica growing on Hualalai, Big Island of Hawai'i.
Prickly pears are the only type of cactus normally found in the eastern United States, and are the most cold-tolerant of the cacti. Species normally found in the eastern U. S. are:
- Opuntia fragilis -- little prickly pear, found in the northern Great Plains and as far west as British Columbia, also found in the southern Great Plains
- Opuntia humifusa -- eastern prickly pear, found throughout the U. S. east of the Great Plains and into southern Ontario
- Opuntia macrorhiza -- plains prickly pear, found throughout the Great Plains except for the northernmost areas (not found in North Dakota, and extending sporadically eastward as far as Kentucky.
- Opuntia basilaris - commonly known as the Beavertail Cactus is found in southwest USA and northwest Mexico.
A species of prickly pear (Opuntia stricta) was imported into Australia in the 1920s for use as a natural agricultural fence and quickly became a widespread weed, rendering four million hectares of farming land unproductive. The Cactoblastis moth, whose larvae eat prickly pear, was introduced in 1925 and quickly and almost wiped out the infestation. This case is often cited as a textbook successful example of biological pest control.